i know what you mean. i used to live with one (my sister's roommate) before moving and he took most of my gear. so i quit the game(after that and a few fights with them.) came back a year later and switched servers
then on the new server met this guy who friended us(me, my bf and my brother) and got us to share account info with him i met his girlfriend first and i used to compound stuff for her and also was her compounding teacher. then met her bf, friended him shared password and stuff and lvled each other if one was away most times it was my bf and i doing the lvling for everyone. later to find that i, my brother and my bf all had gear, gold and IM's missing all stolen my the girls bf. she eventurally broke up with him but he still went around getting a new gf every week or month or so and taking their stuff. even had igg questioning my friendship with him cause i bought him points before and then fouund out about half the server was involved with him and tricked by him into getting ims and gear till some one reported it and igg would block us every time we tried to get points and we had to submit a report everytime to say that we owned the account and who we're buying points for even if we're vips buying for ourselves it totally sucked. all cause of people you know and come to trust.
aniways moved out of home now and switched back to my old server... funny... questionging if i want to trans my chara or just quit this game for real this time.