While that may be the main trust factor, you should also read previous posts of the user to see if there has been conflicts in the past.
You should also check the reason when seeing a negative iTrader. Just like mine, suddenly yesterday someone thrown a negative itrader to me, I don't even know him, never had any business at all with him. Darn!
Users submitting itraders where no transaction took place or out of the blue are subject to account termination. Contact the staff and they should assist you.
My iTrader has turned to 0, I swear I had at least 2 or something when I got some work done about a year ago. Does anyone know if it resets over time?