If someone wants to tip me, they can. If not, I don't care.
The only thing I require is that they ask me. If they don't and they open a trade window, they get put on ignore, and then I proceed to tell all the other rogues that I know on my server to put them on ignore too.
As far as tips go, I've gotten anywhere from 10s to 10g. I don't really care because it's easy to do; the one that pisses me off is when people whine about me charging them 5g for a gem cut (no matter what the gem is).