New tires are used already?

That was my thinking when I replaced the Tow Max tires on the two year old used trailer the year after I bought it. The tires had a bad reputation and I didn't know how they were treated before I got them. I put Carlisle Radial Trail and went from a load range E to a load range F. I weighed the trailer and was well under the load rating, ran at max. pressure (checked every trip),drove under the speed rating and never abused them. At three years I blew two of them. I think they are poor tires and age is more of an enemy than abuse.
Brian