If there is any reason to have a deal with you, it will be because of your membership level and your trust rating.
Account like this he can buy for 0.5 BTC - if there already is invested 1.5 BTC he is on + anyway..
It can be easy to assume such things.
I can verify ownership by associating myself to the people I have dealt with in the past (that have provided the feedback). I live at the same address if any of the people that sold me GPUs last year would care to visit.