I wouldn't sell to them ever. If the person that buys your account off them claims it was recovered (even if its not) they will charge you back and unless you can actually recover the account and sell it again your down some cash.
I havent used them in forever but I would buy gold farming and slowly take a couple mils here and there and they usually wouldnt notice. Now they seem to notice. Apparently they buy accounts legit but I have heard tons of horror stories about gold4fun.