Most of this is crap, 2nd hand tyres are shipped in lorries to the UK as the laws over there are different due to having autobahns. If you puncture a tyre, even as you leave the forecourt in Germany you have to replace both sides for new.
Hence they have a massive surplus of near new tyres. Couple that with the requirement to run winter tyres on your vehicle then there are a lot of good ones survive.
And fixing a tyre (nail hole) does nothing to weaken a tyre at all.
I got 4 x Conti Winter Contacts with 7mm on for 120 fitted and new they are £150 each for 225/55/17’s.
I wouldnt pay new prices so they are better than the summer tyres even if slightly worn