Yes, a tricky one. I must admit I am not keen on flying with people unless I know their "history", and nowadays I almost never do so.
A very wise thing and pretty much the same as me. I am very wary of flying with people I don't know, and would almost never sit in the back unless there is someone up front I completely trust, know their experience or the way they fly. This stems from several incidents post PPL with other low time pilots from showing off to bad decision making which could have ended very differently.