Buyers are entitled to their opinion and negative feedback can be a wakeup call. Hundreds of positive notes flood in and there in the middle of the pile is one negative one. Was it something I said or something he did? Was the product less than good? Did you describe the rust, the dings, the colors as appropriately as possible? All those questions fly through the head of the seller. I think this is a good thing.
Take the negative and move on.