I have bought and sold used tires. If they are not on rims, you can see if there is damage, to the inside (can't hide that). But if you know nothing about tires, I'd avoid it.
I dislike the newer width/percentage measuring method. The old method was so easy and your tires were simple to figure out. A 33x12.50/16 was a 33 inch tall tire that was 12 1/2 inches wide for a 16 inch rim. Easy!
My drag tires, on the rear are dimensional tires while every other one is %. If you want to change widths you have to find out from the manufacturer if their specific tire will be taller or shorter, because the % is never right on. The math may say it is one thing but in reality, it is quite different. So frustrating. It is so common, handheld tuners do not let you enter in your tire size. They go by "revs-per-mile" and the math won't work on that either. I use my GPS to figure actual MPH and make a fraction that allows me to tell the tuner, next time I stop, which direction to change the RPM.