Have you ever been in a PuG raid where everything goes shit and thought "there were signs of this, why didn't I react sooner!".
Yes, there are signs. Signs that scream "this is surely going to fail!" and we always think "naaah, it's probably just an honest mistake, that warrior has gemmed spirit because...". Well there's no excuse for that really. But for some reason we tend to stick with something, unless it really really fails at once.
I'm not trying to promote ditching something as soon as there is a wipe, or someone dies, like some people do. But some things are just too horrible to ignore, and if you want to spare yourself the frustration and ruined evening, you should go with your gut feeling that says... "Get out of here... while you still can".
Here is a list of things to look out for. If you have anything on this list in your raid, you should be very cautious. If you're lucky it's an isolated incident and you can just fix the problem. If you're unlucky and have more than one of these in your raid, you seriously should think about "disconnecting".
1. The hunter says he is a "melee-hunter".
2. Raidleader doesn't know how to turn of caps.
3. Main tank says "mom says it's dinner soon".
4. People try to lose aggro by running away from the tank.
5. The paladins use only minor blessings.
6. The main tank uses BoA-gear.
7. The raid leader says "this is an rp-raid".
8. The tank healer says "I have really bad lags".
9. The raid leader isn't part of a guild.
10. More than half the raid use "Jenkins" title.
And there are tons more, so I'll surely make another list later. Can you think of any more sure signs that a raid is going to fail?