Well, a lot of the time, it's difficult to know who will be a problem player before any actual play has occurred, but there are always a couple red flags you can look out for:

• Ask the player what kind of character they want to run in your game. If they give you a description that's in stark contrast to the setting you've described, the two of you may have clashing expectations pertaining to the campaign you want to run, and you and that player might struggle to tell and enjoy a coherent story. Offer a few suggestions to help that character better fit the setting, if possible, and if it's just way out of left field, ask if there's maybe another character they'd want to play that fits the tone of the campaign. If they're unwilling to compromise, they're probably not a good fit for your group.

• During session 0, pay attention to how they interact with the other members of the group. Are they making inappropriate or off-putting jokes? Do they talk down on other players, or their character ideas? Do you just get a weird vibe? If you're closer friends with another member of the group, bring it up after the fact - just ask what they thought of the new guy. If you feel like something's up, you'll likely hear it from other people too.

• Following session 0 and the commitment to create characters prior to session 1, ensure that your player responds in a timely manner. If you're closing in on session time (24-48 hours or so beforehand) and you still don't have a sheet, ask if they need any help with character creation. Sometimes they do genuinely need the assistance figuring out features or setting something up in a VTT, and on rare occasions you might get a reasonable excuse from the player for not being prepared or able to make session 1 - life comes before the game, after all - but if you get a lukewarm response from them or an apology and some vague pledge to be ready by game time, take it with a grain of salt; those players tend to be very flaky, and even if they make session 1, you may have attendance issues down the line.

Ask my friends who wants to play. I'm not friends with people who cause problems ¯\_(ツ)_/¯

Step 1 : post about the game with every info I would like to know as a newcoming player Step 2 : a form to weed out people not interested enough to fill it and with a few questions about their style. Step 3 : vocal interview. A must ever since I okayed a player per writing and found out at session 1 that their voice was so fucking annoying to me. Step 4 : session 0 where you check if everyone is on the same wavelenght or not and where you set your boudaries abour your table Worked pretty well for me.

With desperation.

Not completely a joke unfortunately. Often if someone is interested in the niche game I want to try running and is available when I can run it I'll take them. There is of course some vetting: a light conversation about the system, their interest in it and then I'll judge their reaction and openness to safety tools. After this I can be fairly certain they aren't complete asses.

Also it is easier to endure that player if you don't plan for the campaign to last beyond 5-10 sessions. A dip into the system to try it out and then onto the next one.

Everyone's situation will be different of course, but here is mine.

I have a long-standing gaming group with 2 buddies from high school and have been playing with them since the 90's. The 3 of us are the core of the group. Over the years, other players have come and gone. For those players, we invited them to our regular group after first playing with them in one shots or short campaigns ran for new players or similar. If we have a seat open (our group is usually 6-7 including whoever is GM), we will invite them if they are good people. In the 30 years we've been playing together, we've never had a problem. The only reason people tend to fall out of the group has been people moving or having kids.

I ask my existing friends if they're down for a game, choosing players who I think their personality would match the campaign concept. Even if they've never played before, if they're at least lightly nerdy, I don't work with them, they live within 40 minutes, and have some free time in their schedule, I ask. Then we spend 6 months scheduling a session, spend half of every session trying to remember what happened last time, do that 3 or 4 times until the campaign peeters out because someone's scheduled changes or they move or have kids or something ¯\_(ツ)_/¯

Thanks all for your feedback, Here is my typical technique

Run a couple of "discovery" one shots, the goal is for me to get some practice with the rules, and for the PC to discover the game without any other request.

Do a long post on the forum (my club still use those), where I explain the kind of campaign I plan, including duration and agenda, and no show policy

Based on the answers, the one shots, sometimes feedback from other people, I set a group. (Usually, it's not that much choice anyway)

Session zero is a last "cleaning" moment, where sometimes we see that people aren't aligned

But I already got group exploding mid-flight.

Also sometimes, I take the freedom to remind the shy players that "XXX talks a lot, but feel free to stop them" so they don't feel left out

Interview with my existing crew present. I'll throw out some oddball questions then trust my buddies judgement.