This Is The Flakiest Players Have Been From Roll20

[animorte]

I will admit I'm heavily thinking about telling such people that I need to properly vet them and they need to apply like 2 hours before the game for me to do that.

I think this is a very good idea. It helps to keep you and them from feeling rushed and unprepared.

I personally don’t have a problem improvising (one of the most fun sessions we ever had was a one-shot I had no idea I would be running and I threw together in <10 minutes), but that doesn’t mean other people are equally comfortable.