If the pug leader doesn't announce the loot rules at the beginning of the raid, leave.
If the pug leader doesn't look at the comp, if he doesn't have good gems/enchants, leave.
If the pug leader doesn't speak good English, leave.
If the pug leader doesn't whisper you back in a couple of seconds, leave.
If the pug leader insults the raid anyhow, leave.
If the pug leader speaks to his friends in his own language, leave.
What I've learned from pugs. Have fun =)
Later edit: If you ever attend a pug, do the following:
1. Take screenshots of the initial loot rules + MS changes. Never ever forget it.
2. Take screenshots of every loot + rolls for the specific item.
3. Take screenshots whenever somebody from the raid leaves. It will save you time and space and drama.
4. If your PC has the power to video, do it.
All the evidence you have is a major improvement to the ninja community.