I don't vet the horses that I buy because it simply doesn't make financial sense in my business model. There are times that I will xray a horse after I buy it just to have a set of films if I think buyers may question something (mainly ankles). I try to cut down on the risk by only buying from people that I know and trust and researching every horse using every piece of information possible (google, race record, forums, trainers info, jockey info, etc). I look closely at the pictures and video of the horses. I try very hard NOT to buy horses with lumpy ankles unless they have xrays available as I do find ankles tend to be where I find the most issues. Knees can be a bit harder because you can't always see calcification or changes in the pictures but I do ask for side and front view of the legs. I won't discount a horse that appears to be body sore but there is a difference between that and lame and I think it takes an educated eye to tell the difference. If I have a choice between one that jogs down great and another that looks like it will need a few months of turnout then it is an obvious choice which direction I will go. In my experience, good trainers know the horses well and will tell you if something is bugging them or if they have had an issue. I know the trainers that I deal with don't inject/tap and medicate to get them to the races. I have done enough networking/homework that I only deal with people who I trust. Trust me when I say I have done my time and been burned enough times to get a well earned education in who to steer away from and quite a few of those that I will never ever buy from are frequent sellers on the many facebook groups.
I had another lovely 3yr come in this year that had only ran a few times and was just as slow as could be. He looked absolutely perfect from the outside. Flexed sound. Lunged sound. Never had an issue his whole life. Owned by his breeder. Upon vetting both ankles had small ocd chips in the front. They were smooth, round and the joint was quiet. Likely had been there his whole life. I had paid $2500 for the horse but now I was presented with a horse with an ocd in both ankles. What do you do? I offered him for free to the people who vetted him and they chose to have them removed as it was an easy surgery. They looked at it like all horses have something but his joints were clean and he had no damage so they would easily spend $5k on another horse as nice as this horse plus the risk of vetting a lot more horses just to run into the same issues upon vetting. They took the horse and had the surgery done and he is doing super. Now would most people do that? Likely not but I could see their reasoning.
Recently, I had a horse vetted that also had a ocd chip in the front of the ankle. It was also smooth, round and the joint was quiet. The buyer passed so I reached out to a few of my contacts that I know don't mind a quiet chip and he was purchased for a price lower than I paid for him but someone felt lucky to get a nice horse. They could do the surgery if they wanted to but they may also just leave it.
When findings show up on horses I do disclose them to future buyers. Sometimes they are just so minor that I don't find them to be any cause for concern. What some buyers find to be a big deal others won't even be bothered by! I had a buyer pass because a horse had a scar on his chest and old pinfire marks on his hocks. She was doing resale and thought future buyers might find it to be an issue and I understood but we couldn't fault the horse for that. If I have xrays available then I will provide them with horses. Many people will allow you to have the xrays from their PPE and others will not but you can at least say the horse was vetted and this is what was found.
Vettings are always very subjective. They are just a glimpse at a horse at a moment in time. I have had horses fail vettings because they flex off and later the horse is fine and passes another vetting with totally clean xrays. It isn't the vet's fault because maybe the horse just wasn't quite right that particular day. In those cases I am not going to disclose anything because I know the horse is sound and just was off for whatever particular reason. I have had horses do dumb stuff like tweak something in the field and be sore for two weeks and then be perfectly fine or ill timed abscesses that don't necessarily present themselves enough to conclude that is the issue. I think you do your best to know your horses and be honest but at the same time realize that horses are not machines and things do come up that are not a big deal. Some vets will find something on a xray that they think is a big deal and another vet doesn't feel bothered by it at all. In those cases all you can do is present the information to future buyers and let their vets sort it out.
I do spend some time thinking about horses that I personally know have been vetted by friends and customers that have fairly major issues and are unsound (which to me is a big deal...because being sound with a finding is different that being unsound with a finding) yet are still being marketed at the same price and said to be sound. No mention of the issue despite the seller knowing that the issue is there. I mean if the horse has a fracture how can you advertise it as sound? That kind of stuff really bothers me when there are plenty of good sellers out there that I know will do the right thing even when it means losing money, giving a horse away or euthanizing a horse because it is the right thing to do. None of us are perfect. I have sold horses that later were discovered to have issues or have things turn up but I can honestly say I really didn't know about them. If I know then I am disclosing it! All I can say is do your research. Nobody is perfect but look to see if a person has a history of disclosing issues on horses when they are found or if they try to sweep things under the rug.