Big warning sign for me is when the GM doesn't put all the information you [i]need[/i] out there in the open but still expects you to adhere. Had this happen a few times, and it often leads to 'little' things being left out of their narrative when the roleplay starts proper, only to get thrown in your face like an invisible smoking gun.

I tend to get antsy about a roleplay when more than half of the characters have an 'edgy' backstory. Tends to turn into a power struggle for who can narrate their angst better. 

That being said, I haven't been in enough roleplays on the [i]Guild[/i], so I can't speak to the community here.