Some people ramp up home-brew so much that it's not really that fair. Some people add endless benefits to their spells and then use them. Is home-brew really that fair?

Depends on the homebrew.

If it is balanced it’s fair.

I'm going with IamSposta on this: it depends on the homebrew. It also depends on the campaign.

Homebrew can be a lot of fun, and 5th Edition has seen a huge amount of it because 5th Edition is easier to balance and customise than previous editions or super number-crunchy systems like Pathfinder.

Of course, people will want to "be the best at D&D" and make imbalanced homebrew, or have an idea they'll find fun to play but doesn't fit in the D&D balance mechanics. This is why the DM has final say and should review all homebrew very carefully.

However, it can also depend on the campaign. If the campaign itself is designed to be super-epic high-fantasy -megaheroes against ultimate villains.. Then the seemingly OP homebrew suddenly becomes perfectly balanced. I've known of (but have not played in) campaigns that were basically Medieval Dragon Ball Z. There are campaigns where characters begin already at 20 and are gods going up against cosmic threats. So even for normally OP homebrew, there's a place for them in the right campaign. Even the utterly whackadoodle could still be fair in a game specifically for being silly. 

Homebrew can also "fix" where current options are lacking. Like, more acid spells for Black Dragon sorcerers. Usually taking an existing spell and reskinning it to a more draconic/elemental flavour that is more thematically fitting - while remaining perfectly balanced for a normal D&D game. There's a section in the DMG specifically for homebrewing up some new options and goodies - so some homebrewing is actively encouraged.

So really homebrew can be fair or unfair - depending on the campaign and DM.

Quote from Cyb3rM1nd >>

I'm going with IamSposta on this: it depends on the homebrew. It also depends on the campaign.

Homebrew can be a lot of fun, and 5th Edition has seen a huge amount of it because 5th Edition is easier to balance and customise than previous editions or super number-crunchy systems like Pathfinder.

Of course, people will want to "be the best at D&D" and make imbalanced homebrew, or have an idea they'll find fun to play but doesn't fit in the D&D balance mechanics. This is why the DM has final say and should review all homebrew very carefully.

However, it can also depend on the campaign. If the campaign itself is designed to be super-epic high-fantasy -megaheroes against ultimate villains.. Then the seemingly OP homebrew suddenly becomes perfectly balanced. I've known of (but have not played in) campaigns that were basically Medieval Dragon Ball Z. There are campaigns where characters begin already at 20 and are gods going up against cosmic threats. So even for normally OP homebrew, there's a place for them in the right campaign. Even the utterly whackadoodle could still be fair in a game specifically for being silly. 

Homebrew can also "fix" where current options are lacking. Like, more acid spells for Black Dragon sorcerers. Usually taking an existing spell and reskinning it to a more draconic/elemental flavour that is more thematically fitting - while remaining perfectly balanced for a normal D&D game. There's a section in the DMG specifically for homebrewing up some new options and goodies - so some homebrewing is actively encouraged.

So really homebrew can be fair or unfair - depending on the campaign and DM.

 Absolutely 

If a spell is really that in unbalanced, then the DM can either ban it, or change its level. But I agree with cybermind, and that sometimes spells can be overpowered at first, then prove balanced.

Best way to make it "fair"; only the DM should homebrew anything in a campaign.  From scratch, not "look over" somebody's else's homebrew stuff, whether from a player at the table or from a "reputable" source on the internet or 3rd party publisher.   Only the DM knows the theme, setting, secrets, mechanics, NPC's, etc. of their particular world, even if it is a published setting.

Quote from Pedroig >>

Best way to make it "fair"; only the DM should homebrew anything in a campaign.  From scratch, not "look over" somebody's else's homebrew stuff, whether from a player at the table or from a "reputable" source on the internet or 3rd party publisher.   Only the DM knows the theme, setting, secrets, mechanics, NPC's, etc. of their particular world, even if it is a published setting.

 As a DM I would have no problem with my players homebrewing spells, I would have to approve it first though. Back in the day, Wizard Players we’re encouraged to develop their own custom spells during “downtime activities.”

also depends on what you mean by 'fair'.  fair as in balanced to every other spell int he game? fair as in one player can use it but the other can't?  fair as in the DM and players know about it ahead of time and can develop a strategy to counter or deal with the spell?

Quote from IamSposta >>>>

 As a DM I would have no problem with my players homebrewing spells, I would have to approve it first though. Back in the day, Wizard Players we’re encouraged to develop their own custom spells during “downtime activities.”

 This.

Quote from AlexandraMelianne >>

Some people ramp up home-brew so much that it's not really that fair. Some people add endless benefits to their spells and then use them. Is home-brew really that fair?

 WAY too broad a question. 

* Not all homebrew is created equal. Some of it is quite creative and at a similar power level to the published material. Some of it is "This greatsword gets a +15 on attack and damage rolls, and does an additional 6d6 damage of either fire, cold, lightning, necrotic, acid, poison, radiant, thunder or force, your choice." And everything in between.

* What's "fair" is whatever your group decides is fair. One of the best things about D&D is that you are free to adjust the rules to match your group's desires. The important thing to remember for any homebrew is that all the players(including the DM) need to be okay with it.  

Ok. I get it.

If you look for homebrew spells on any D&D related website, I'd say about 90% of the ones you find will be over powered and the majority of the rest are mostly pointless.

I only allow my homebrewed spells and other content in my games, but if the players want to homebrew something, I make it with them. They don't make it, they tell me the idea, and I make it for them. 

Homebrew is normally broken and terrible, at least in my experience. 

If I'm DMing and a player's created their own spell, subclass, etc, I'll look over it, make sure the concept isn't OP, can't be achieved within the existing rules, and fits with the setting, and then allow it if it's reasonable. Creativity is good! But I wouldn't allow homebrew created by someone I don't know and taken off the internet.

What’s the difference between perusing and approving a player made homebrew and one they found? If it meets all of your criteria, what’s the difference? I also, as DM, also reserve the right adjust anything I see fit to rebalance any homebrew, even my own.

Good question! It's because if a player goes out of her way to write her own material, it shows she really cares about her unique concept, whereas if she found it online, she probably just went "okay, that one's cool, I'll do that one," at which point she really might as well just pick an official one. I generally dislike homebrew in my games, I think the classic archetypes represented in the rules are more than enough for a good game, but if it's a player's "labor of love," I can make room for that.

Fair. 

Yes, making a player or a DM make a homebrew spell or item makes it so the player doesn't get in their mind that they can go to whatever D&D website they want and choose 100 random spells and magic items they want to make or use, and that it'll be okay.

I specifically only use Homebrew that I deem as balanced (Blood Hunters for example), widely used, or made by me or under my supervision. 

I know how bad homebrew can get, so I don't allow it unless the players understand that it is rarely used. I know this sounds weird, but it does keep players from trying to use any homebrew that they want whenever they want. That's how I avoid players wanting to be Flumph Sumo-Wrestlers that can cast Melf's Major Meteor Swarm.

Understandable. My players aren’t that bad, so if I say “anything in reason, pending approval, subject to change” they understand it. To be honest, I encourage Wizard players to come to me with homebrew spells that their characters want to “create” just like back in the old days.

Quote from IamSposta >>

Understandable. My players aren’t that bad, so if I say “anything in reason, pending approval, subject to change” they understand it. To be honest, I encourage Wizard players to come to me with homebrew spells that their characters want to “create” just like back in the old days.

 If Wizards in my games want to make their own spells, I help them make a balanced version. That definitely is allowed, but they have to realize that it is hard to do so, and takes a long time, and they have to be their own ideas for spells.