You are free to leave whatever feedback you wish, and you should honestly not feel forced into leaving something that does not reflect your experience. Vendors are completely free to talk amongst themselves - this is a free community, after all, and they are entitled to freedom of speech like the rest of us. If they wish to keep a 'Vendor's Blacklist' amongst themselves, they are free to do so. Buyers are also free to keep a 'Buyer Blacklist' listing all the vendors that partake in such activity if they wish, so it does work both ways. If you feel so strongly about it, perhaps consider starting a thread in the Rumor mill forum listing the vendors that you have clear evidence for that do this? Freedom ensures fairness! Libertas