I wear my two negatives as a badge of honor. Very similar situations to yours....I was the buyer on both and got junk when I paid for mint, and the seller blew me off. In the comments section on both transactions, I left something like "Retaliation feedback-He has my money, and I have his crap "mint" chip-you figure it out!"

I don't like to see the good guys and gals get screwed over then worry about posting a negative because they will be getting a negative in return. We may as well not leave any feedback if it comes to that. One negative every 100 transactions would not deter me from doing business with someone.