Don't take it personally. This is Discoweb, where diplomacy often takes a back seat to directness (or talking shit, as you put it). You are selling a set of used tires, not some interior trim piece where age doesn't affect the safe operation of the vehicle. Is it unreasonable for a potential buyer to want to know when the tires were manufactured before spending $550? In my experience transparency on the seller's part results in a more satisfying transaction for everyone. If you are unwilling to provide the date of manufacture then don't be surprised if (a) people question your integrity, (b) you don't sell the tires, or (c) both. How long would it take you to walk to the garage, find the date code on the sidewall, take a photo, and post it? Does it contain information you wish to conceal? A defensive attitude and reluctance to share basic information about your tires doesn't exactly inspire trust. The good news is that it's easy for you to change that, but it's your call.