... is sellers who say they will leave you positive feedback once you have left it for them.
Look, I've bought, I've accepted your terms, I've paid - usually as I won the auction. If I've done my bit, you have no reason not to give me positive feedback straight away - regardless of my perception of you. Isn't that right? If I've done my bit, is it acceptable to suggest that you will only give me good feedback if I also give you good feedback?