Well i usually report them, however i have a new tactic :P

1) Find them (the easy part)
2)SS or make a vid.
3)Blackmail them (yes i said BLACKMAIL)
4)After receiving the money/items...Report them ];-)
5)Evil Laugh. example: Muahaha

Example with Screenshots:

Steps 1&2 on this SS

Look how he says he isnt one, but when i mention the gs, he starts begging ]:)

Steps 4&5 on this one

First he offers 7k in gold, so i ask for more. In the end i get 7k in gold, 5 MS, 2TA, 3 drake eggs, 1 pan flute and some scrolls.
2 mins later i warned a gs on the shoutbox.

Now, who said evil doesnt pay???

*Muahaha*