Some guilds simply go by attendance numbers; if you've shown up consistently, you're in. If you just happen to be making an appearance for farm night, you're out. Some guilds pick based solely on performance in the raid itself; if you're consistently pulling high DPS and not standing in fire, you're in. If you can't find your way out of a poison cloud with a map and GPS system showing you the way, you're out.
But what do you do when you're the one being sat?