Lying is an art. Communicating without revealing any intents behind is key, which is sometimes easier by hiding your facial expressions, eyes looking behind DM screen or in book, etc.. Or appearing to read the info from notes can look more truthful. Speaking on common tone, and often quickly chaining with saying something else can pass something more easily.
Later you can always tell them something is amiss or doesn't sound right, with or without checks. A successful Wisdom (Insight) check or Intelligence (Investigation) check bring up new interrogations or assumptions on a revisited subject. Pushing them to question something they previously thought was true is also a good way to cause them to reconsider the veracity of something.
Paranoid players are hard to work around, so good luck if that's what you're working with. But in general, players will take a lot at face value if you don't give them a hint not to. Loud people, friendly people, or apathetic people tend to come across as pretty believable.
Something I like to do to convince a falsehood, is try to describe it to someone who has never seen anything like it. An example is when I described a wolf to someone who came from the shadowfell. Dark and rigid, with eyes more ready than any beast you've seen. Fur that acts under a pattern, flows with the wind. Legs that refuse to bend under its weight. It seems so much more frightening when you don't know what it is. So taking an approach like that can make a player feel like theyre seeing the truth as they've seen it. Everyone tends to believe what they see, so describing what they see as they see it comes across as objective truth.
Finally, you have the chance to prepare. Lying is always easier when you can plan ahead. My advice, say the lie in character as though it were the entire truth. Pretend the character believes what they're saying. Pretend to be the person the character is pretending to be. It kind of tricks your mind into seeing it as true, so it's harder to imagine as a lie. And you can't be caught in a lie if you believe it's true.
My final advice is making sure you know the reason for the falsehood. Knowing exactly why it's a lie, exactly how it's a lie, and what is meant to be the give away makes it easier to tell a convincing lie that foreshadows the twist.
How do you convince a player/party that something is true while also giving them the capacity to think later that something might have been amiss?
Very carefully. A couple rules. First the PCs will either trust the information or ask for an insight check. How you respond to the insight check can be important.
Unless you introduce new information the players are unlikely to change their opinions on the above.
Remember that statements can be misleading and entirely true. Recently I had players believe an NPC was a vampire. The asked another NPC if the person had been seen in the daylight, to which the NPC said yes.
The important thing here is the specific words everyone said. Vampires don't have a problem with the daytime, only with daylight.
In a lot of ways, you don’t. For me, I just tell them, your character sees (or hears or reads) this: then fill it in. The conclusions that the player and character draw from that information are out of your control. Sometimes they guess right, and good for them, they’ll feel great when it turns out they were right. Sometimes they’ll be wrong, but even then, usually, hopefully, they’ll feel great, because they appreciate what they misunderstood, or how they were deceived.
I wouldn’t, personally lie to them. An NPC may lie, or an NPC may be wrong or misinformed and give them information they think is correct even though it’s not. But as a DM, I wouldn’t lie to the players. It’s a big distinction between players lying (the DM is a player) and characters lying.
The thing to remember is: You (the DM) should not be attempting to deceive the players. Rather, your NPCs are attempting to deceive the PCs, and you are simply conveying the situation as it appears to the PCs. It may be useful to get into the habit of using weasel words such as "appears" even when no deception is involved.
I would ask what the reason behind the lie is. Does the person telling the original story believe the information is true? If so, any Insight checks you make should show that. If the person is knowingly lying (and you want the party to believe them), then it becomes trickier if you rely on dice rolls.
Later on, is there evidence that the lying person discovers that makes them realize they were incorrect? Does the party come across other information?
Already a lot of good advice, but there is one trick of the trade I didn't see mentioned.
Make certain dice rolls in secret. This is a good practice as certain situations are give-aways if you know the results of the dice, sometimes even if you don't, hell sometimes even just knowing that a roll was made says a lot, even if done in secret. Some examples include Stealth, Perception and Insight checks, these types of checks when a player knows are happening or knows the results (or even if they don't) gives them a ton of information that is very easy to deduce what is happening.
The classic "make a perception check" and then seeing that you failed, clearly tells the players "there is something here we missed". Even if you make this check in secret, if the players know your making a perception check, that already says a lot.
So its a good practice to make checks behind the screen without saying a word, sometimes even randomly for no reason just to get players used to the idea of "there is stuff happening we don't know about".
A good example of of dealing with a lying NPC is that when players are having a conversation with an NPC, suddenly make inexplicable hidden check behind the screen, but say nothing about what you were rolling for or why. Even if they have absolutely no information, you will have their attention. Its a good way to signal that something is up. Its important however to always do this, even if nothing is up at all, just as a habit, aka the fake roll.
This is a good practice because it signals to players that "hey, there is stuff happening behind the screen you don't know about... all the time and you need to be thinking and paying attention, all the time.. there are no breaks or freebies".
All that said... there is one piece of advice I give over and over again and its so critical to good DM and aleviating the frustrations of being a DM.
It is not your job to care what the players do or don't do or believe or don't believe. This doesn't matter. You don't need to convince them that someone is telling the truth or is lying or worry about either. This is a collaborative storytelling game and you cannot and should not control any aspect of what the players are doing or thinking. That is not your job and should not be the source of frustrations or any feelings at all. It is, basically irrelevant to being a DM. You are a narrator not a story writer.
How do you convince a player/party that something is true while also giving them the capacity to think later that something might have been amiss?
Forever DM and perpetually online
Second-In-Command and Acting Master of the Underground
Lying is an art. Communicating without revealing any intents behind is key, which is sometimes easier by hiding your facial expressions, eyes looking behind DM screen or in book, etc.. Or appearing to read the info from notes can look more truthful. Speaking on common tone, and often quickly chaining with saying something else can pass something more easily.
Later you can always tell them something is amiss or doesn't sound right, with or without checks. A successful Wisdom (Insight) check or Intelligence (Investigation) check bring up new interrogations or assumptions on a revisited subject. Pushing them to question something they previously thought was true is also a good way to cause them to reconsider the veracity of something.
Paranoid players are hard to work around, so good luck if that's what you're working with. But in general, players will take a lot at face value if you don't give them a hint not to. Loud people, friendly people, or apathetic people tend to come across as pretty believable.
Something I like to do to convince a falsehood, is try to describe it to someone who has never seen anything like it. An example is when I described a wolf to someone who came from the shadowfell. Dark and rigid, with eyes more ready than any beast you've seen. Fur that acts under a pattern, flows with the wind. Legs that refuse to bend under its weight. It seems so much more frightening when you don't know what it is. So taking an approach like that can make a player feel like theyre seeing the truth as they've seen it. Everyone tends to believe what they see, so describing what they see as they see it comes across as objective truth.
Finally, you have the chance to prepare. Lying is always easier when you can plan ahead. My advice, say the lie in character as though it were the entire truth. Pretend the character believes what they're saying. Pretend to be the person the character is pretending to be. It kind of tricks your mind into seeing it as true, so it's harder to imagine as a lie. And you can't be caught in a lie if you believe it's true.
My final advice is making sure you know the reason for the falsehood. Knowing exactly why it's a lie, exactly how it's a lie, and what is meant to be the give away makes it easier to tell a convincing lie that foreshadows the twist.
Very carefully. A couple rules. First the PCs will either trust the information or ask for an insight check. How you respond to the insight check can be important.
Unless you introduce new information the players are unlikely to change their opinions on the above.
Remember that statements can be misleading and entirely true. Recently I had players believe an NPC was a vampire. The asked another NPC if the person had been seen in the daylight, to which the NPC said yes.
The important thing here is the specific words everyone said. Vampires don't have a problem with the daytime, only with daylight.
In a lot of ways, you don’t. For me, I just tell them, your character sees (or hears or reads) this: then fill it in. The conclusions that the player and character draw from that information are out of your control. Sometimes they guess right, and good for them, they’ll feel great when it turns out they were right. Sometimes they’ll be wrong, but even then, usually, hopefully, they’ll feel great, because they appreciate what they misunderstood, or how they were deceived.
I wouldn’t, personally lie to them. An NPC may lie, or an NPC may be wrong or misinformed and give them information they think is correct even though it’s not. But as a DM, I wouldn’t lie to the players. It’s a big distinction between players lying (the DM is a player) and characters lying.
The thing to remember is: You (the DM) should not be attempting to deceive the players. Rather, your NPCs are attempting to deceive the PCs, and you are simply conveying the situation as it appears to the PCs. It may be useful to get into the habit of using weasel words such as "appears" even when no deception is involved.
I would ask what the reason behind the lie is. Does the person telling the original story believe the information is true? If so, any Insight checks you make should show that. If the person is knowingly lying (and you want the party to believe them), then it becomes trickier if you rely on dice rolls.
Later on, is there evidence that the lying person discovers that makes them realize they were incorrect? Does the party come across other information?
Already a lot of good advice, but there is one trick of the trade I didn't see mentioned.
Make certain dice rolls in secret. This is a good practice as certain situations are give-aways if you know the results of the dice, sometimes even if you don't, hell sometimes even just knowing that a roll was made says a lot, even if done in secret. Some examples include Stealth, Perception and Insight checks, these types of checks when a player knows are happening or knows the results (or even if they don't) gives them a ton of information that is very easy to deduce what is happening.
The classic "make a perception check" and then seeing that you failed, clearly tells the players "there is something here we missed". Even if you make this check in secret, if the players know your making a perception check, that already says a lot.
So its a good practice to make checks behind the screen without saying a word, sometimes even randomly for no reason just to get players used to the idea of "there is stuff happening we don't know about".
A good example of of dealing with a lying NPC is that when players are having a conversation with an NPC, suddenly make inexplicable hidden check behind the screen, but say nothing about what you were rolling for or why. Even if they have absolutely no information, you will have their attention. Its a good way to signal that something is up. Its important however to always do this, even if nothing is up at all, just as a habit, aka the fake roll.
This is a good practice because it signals to players that "hey, there is stuff happening behind the screen you don't know about... all the time and you need to be thinking and paying attention, all the time.. there are no breaks or freebies".
All that said... there is one piece of advice I give over and over again and its so critical to good DM and aleviating the frustrations of being a DM.
It is not your job to care what the players do or don't do or believe or don't believe. This doesn't matter. You don't need to convince them that someone is telling the truth or is lying or worry about either. This is a collaborative storytelling game and you cannot and should not control any aspect of what the players are doing or thinking. That is not your job and should not be the source of frustrations or any feelings at all. It is, basically irrelevant to being a DM. You are a narrator not a story writer.