I suspect most people on PinSide - certainly myself included - have had the rug pulled out from under them by a seller at one point or another. It really sucks. That being stated, I personally agree with others that the feedback system shouldn't be used for transactions that never occured.
I had someone on FB Market do this to me with a killer deal on a TFTC; literally five minutes before I got in the car to make a two hour trip they messaged me that the game was sold because 'I hadn't heard from you since yesterday so I figured you didn't want it anymore'. It was obvious someone offered them more money, but what could I do? Leave FB feedback that they didn't sell me private property? There's no contract involved. You have to shrug your shoulders and move on.