When Looking at used trailers make sure you closely inspect the tires or just assume they will need to be replaced. Check dates, sidewall cracks, weight ratings. Also be aware that a lot of used trailers wind up with car or truck tires on them which is very much against DOT regulations. Some years ago Pennsylvania DOT was actively pulling over car hauling trailers and handing out tickets for incorrect tire type and/or weight rating. Probably worse now.