Hi, I am a first time DM. I've been running the Lost Mine of Phandelver from the started kit for a few sessions now. I am playing with my wife and another couple and we're using the starter kit characters. One of the players is the Rogue Lightfoot Halfling and he really likes to take advantage of the con artist side of the character. But anytime the party gets treasure he tries to use deception or charisma or some other random skill to "try and convince" the other PCs to give him more of the treasure. I don't know how to handle it, I almost always shoot it down but he argues with me and sometimes I just give up and let him roll a deception check versus the other players intelligence. But it feels wrong and it leaves the other PCs annoyed and confused. Is this something that even makes sense for one PC to do to another? If it is, how do I handle it?

Thank you, this helps a lot. We didn't have a session 0. We are all new players so we just jumped right in

Just remember, you have absolutely no control over the player's character.  None.  It is inappropriate for the DM to get involved at all in this situation, because you are taking away player agency by telling the rogue's victims what their characters do when they should be.

If the rogue is attempting to deceive another player, it is that player's purview to call for the check, if they decide to, to set the DC to whatever they want, then narrate what their character does.  Never get in the middle of that and threaten player agency.  That is why the other players are confused and annoyed. 

Treasure is the lively hood of adventurers.  That is literally their paycheck for risking their necks.  It would be like someone trying to persuade you to give them a month's worth of your salary in real life.  I, as the player, would ask the rogue to make a DC 45 persuade check to do that.  That's just me.  Your other players can decide how their character reacts.

Bear in mind that the rogue can try to make the check, but even if he succeed on the roll that doesn't mean he automatically succeeds and gets what he wants, it just means that he isn't an obvious fraud.  The other PC's can still decide "No, I'm going to keep this treasure."

Mind you, this does point to there being an underlying out of character problem at the table.  I would pull the player aside and say that while it's nice to see him engage in the roleplaying aspect of the game, he does need to tone it down so that it doesn't impact the enjoyment of the other players, which it clearly is.

I completely disagree with siresamuel. This has nothing to do with player agency. This is one player trying to put one over on another player, then pointing to a die roll and saying, now you have to do what I tell you. Actually if there’s any agency being restricted, it’s that of the person the rogue is attempting to persuade. This is a situation that inevitably leads to player (not character) conflict, and it is not only allowed, but basically expected that the DM should step in and stop this before people start getting angry. 
And it is the DMs purview to call for a check, not the player’s.

To the OP, I agree with lyxen. Have a session 0 — it’s never too late to do, and in spite of the name, doesn’t have to take a whole session. You need to get everyone on the same page about how you will handle inter-party issues, and probably lots of other things, as lyxen said, check out Tasha’s for a good guide to them.

And, as a bit of related advice, I can already hear the rogue’s player saying “but that’s what my character would do.” That is never an excuse. The player needs to understand that they are in a game with other people. They should be allowed to have fun, but that stops when their idea of fun starts stepping on the fun of others at the table. And also point out that if they really want to stick with the “acting in character “ defense” then the rest of the party would likely, in character, decide to stop traveling with this annoying halfling who keeps trying to take more than their share of the loot.

Quote from SireSamuel >>

Just remember, you have absolutely no control over the player's character.  None.  It is inappropriate for the DM to get involved at all in this situation, because you are taking away player agency by telling the rogue's victims what their characters do when they should be.

 This is absolutely NO.

It is the GMs responsibility to keep this crap in check. Unless all of the players are on-board for PvP, what the OP is describing is a no. It is not ok for a PC to do this to another PC. As stated, the other players do not like this and it is making the game unfun. The same goes for spells or attacks, not just skills.

+1, player agency doesn't override rules of the table (stated or unstated).

Furthermore, players don't call for checks. Players say what their PC is doing, and the DM calls for a check.

Quote from SirNoodles78 >>

Thank you, this helps a lot. We didn't have a session 0. We are all new players so we just jumped right in

If you are new players, I strongly recommend that you ban player-vs-player activity of any sort... attacking, skills vs each other, stealing from, any of it. Explain to the players that these things can be done, and can be fun, but you need to be experienced RPers before you try it. Do not try to do it as new players.

Quote from Wysperra >>

Quote from SireSamuel >>

Just remember, you have absolutely no control over the player's character.  None.  It is inappropriate for the DM to get involved at all in this situation, because you are taking away player agency by telling the rogue's victims what their characters do when they should be.

 This is absolutely NO.

It is the GMs responsibility to keep this crap in check. Unless all of the players are on-board for PvP, what the OP is describing is a no. It is not ok for a PC to do this to another PC. As stated, the other players do not like this and it is making the game unfun. The same goes for spells or attacks, not just skills.

Maybe I need to reiterate what I'm saying here; It is up to the player to decide how their character reacts to this rogue trying to swindle them, not the DM.  The rogue does his schtick, looks at the DM for a deception check or whatever, if it were my game I would tell him "What are you looking at me for?  Look to this player you are interacting with.  I'm not going to tell you how they react."  

That player can decide whatever they want.  If they decide their character tells the rogue to buzz off, then fine.  Maybe they decide their character is convinced utterly and completely to hand over the treasure.  Maybe they want to see a roll for the rogue then go from there.  It is their character.  They decide. 

Just to add my +1 to the 'Don't allow player vs player skills like this' side - particularly without consent from both parties. It ends up messy, and competitive, and not a whole lot of fun. Especially for new players, it's good to establish the basic rule that you're all on the same side and generally working together.

That doesn't mean players can't interact with each other, or have lively discussion or debate - but this is one area of the game where the player and their character mingle. The moment you start trying to pickpocket your party members, or use persuasion skills to force players to make their character do things they don't want to and the like, that's the moment players are taken out of their character, and have to resolve things as players. It just doesn't work.

That said, there are instances where skill checks can be used in a player to player setting, to help decide what their character should do. For example, I was in a party of 3, and playing a timid character, with zero leadership skills. The other two were discussing which way they should go in a dungeon, and coming to a stalemate, decided I should have the casting vote. I asked if they could both role a persuasion check to see which my character found more convincing. But I could just have easily asked each of the player to persuade me, as a player.

Ultimately, we mutually decided to let the dice decide. And that was amicable for everyone.

It should be noted that the rogue player can try to convince the other players to hand over the loot, but that's an actual conversation between players who are making up their own minds. People being people, no game mechanics.

 Maybe they want to see a roll for the rogue then go from there.  It is their character.  They decide. 

They decide how their character reacts, in terms of RP, yes. But the players don't get to call for rolls. That is clearly delimited as being in the purview of the DM in RAW.

If you want to let the players call for rolls at your table fine... sometimes I'll let them ask to do them if it is not getting out of hand. But players normally do not do this, and they absolutely don't get to set the DC.