Speed of transaction (sale time, response time, shipping time, payment time)
Happiness with the product (is it in the condition the seller said it was, is it what you expected)
All negative comments obviously need to be about the transaction and not the person selling/buying.
If the shipping was late, just say, Shipping was later than told, and leave it at that. Don't say, Seller sucked dirty assholes because they didn't send me my shit the exact second that the money hit their account.
