I'm a horse breeder and trainer myself. Sometimes I breed and train horses, sometimes I buy them at auction and then train them for reselling. My experience with auctions has always been good, because I always buy unbroken 2-3 year olds with vet checks from vets I know.
So, a few weeks ago a very big auction was selling a horse that looked familiar to me. I rang up the first owner, where we went to check out the horse itself a few months before this specific auction took place. There we found out the horse had severe calcification in multiple spots and Osteoarthritis, so we ended up not buying it as the horse was unfit for the sport.
My surprise was big when I saw a CLEAN vet check on this horse on the auction's website, when the previous vet check found the horse as non-compliant. The first owner sold it to the new owner for an apple and an egg, to then see the horse sold at auction for 4.5 times that amount! This horse will likely become lame if not permanently treated, which is bad for both horse and owner.
Please, when buying at an auction, make sure you get in touch with the breeder/trader behind it first. Check the breeder, if possible. Or the owner. If they're not reputable, just stay away. This is not the auction's fault, it's the trader's fault for not saying it and probably also the vet for taking pictures in an angle where the issues are not visible.
ALWAYS let your own vet check the X-rays. Never ever let the time pressure of an auction push you to a purchase you might regret. Generally a horse that is > 3 < 7 y/o AND is saddle broken, is not put on auction unless it is unsellable otherwise or doesn't jump that well. I never resell at auction, they always get sold off of competitions or through intermediaries. I'd only go back to auction reselling if I need to move inventory fast, which I haven't yet.