you have to remember that every guild is always looking for new members who aren't morons, good players and such you know. I have certain guilds on my server blacklisted from me ever joining (some from me ever even pugging with) purely because of the actions of 1 or 2 people. I know you can't judge an entire guild by a couple people in it, but the fact remains those people were raiding with said guild and were the only members I had any interaction with, so it's my only experience with said guild. Those guilds might even be high-end heroic progression but because of some of the trolls they have, the less intellectual kind that is, I just don't play with them.
I mean there's a line every guild should draw in my book. If you have a dps who sits in tradechat all day spamming the same old annoying trolls, that serves to give your guild a bad rep and limits who will join them. Now some trolls I find interesting, they say genuinely intelligent things, but they're few and far in between.