I don't know why people leave feedback for accounts just because they are bought /sold. It doesn't really accomplish anything in the big picture, and only serves to drive the activity underground, which leads to a lot of people getting screwed over. If people didn't leave negative feedback, people would probably be a lot more open about what accounts are being sold/bought, which would be much more beneficial over the long term than the short term benefits of a few accounts getting bad feedback.
If the "compelling evidence" is made public my feedback will be removed. So far the "buyer" of the account is being shady in my opinion. And the original owner is disputing the sale. Something is up, isn't it?
Maybe it's a bit of a vicious circle... Buying accounts is a pretty underground activity right now. So people don't trust bought accounts and leave negative feedback to warn others. In turn account buyers try to hide.
However, the circle can be broken from both sides. The buyer can take the first step and be transparent about what happened. That could breed enough trust to get the negative feedback returned.
And in this case the negative feedback might accomplish something. I know the new owner is signed up for a signature campaign. The negative feedback thing may get him kicked out of that. I hope it will give them an incentive to resolve this particular issue openly.