A few years back, my dad needed a set of tires for the MKZ I now own. A local shop talked him into a set of claimed "barely used" Michelins that "the first buyer didn't like."
I bought the car from him about a year later, and when I got it that set of tires was so badly dry-rotted that one of the first places I drove it was to a tire store and threw a set of Michelin Primacy MXM4s on it. $1K later, and it rode like a new car.
To be fair, even though I've always trusted Michelins I've heard a lot of mixed reports on them dry-rotting early. The shop I used showed me that they were selling me the "freshest" they had in stock of that particular model, and they were 2-3 months old as best as I recall. I've put 16K miles on them in a year and a half, so I suspect that I'll run out of tread before they really have time to dry rot.
I might chance used again on a high end set of tires, but I'd want to see the date codes and make sure I wasn't paying for a lot of tread on tires a couple of years old. If it were a matter of getting a set of tires on a car to have it safe enough to be sellable, I'd do it.
One last thing-when I bought my MG it didn't have a spare at all, and someone gave a RoStyle wheel with a tire on it that shed rubber every time I touched it. I carried it, figuring it was better than nothing, but when the guy handed the wheel over to me I almost expected to see him make me sign a liability waiver that I wouldn't drive on the tire
. A local shop sold me a used 185/70R14, mounted and balanced for $50. It's a no-name tire, and is probably at 50% tread, but I think is 3 or 4 years old and I'd at least trust it to get me home(or to a tire shop). I don't lose too much sleep over that particular tire. Fortunately, provided that the rim isn't too badly rusted and the shop preps it properly, flats aren't terribly common on the old RoStyle wheels these days. I do need to have one of mine looked at as the left front has a slow leak(I air it up about once a month) but I'm not worried about it blowing out. Folks who run wire wheels with tubes still would be foolish to not carry a spare of some sort.