yes thats right, long time ago( 1.5 years) they tried this on me to. but i had 2 pc's on my desk that time and i followed every step. i came there with 2 of my own chars. once i traded myself("friend") for the first time, he asked me to trade them back to the ("selling") char. at that moment he starts his program. as soon as i hitted trade:
on my 2nd char i see a trade with my 1st char
on my 1st char i see a trade with the scammer
this came on the exact same moment. if you click the trade away, a new one will pop up automaticaly.
only way to get out is ctrl alt del.