My OTTB who is retired has a trainer who got on her WAAY too early and ran her way too fast way to early. The owner didnt understand why it was bad at the time. My girl and all the other horses that were with that trainer were retired due to the same thing. Bone chips in the knees. Luckily my girl has stunning conformation and the gaits and mental attitude of a performance horse so im breeding all around babies out of her. I agree with the unsound horses need to be checked over carefully but sometimes there is a reason why they broke down so early and it wasnt their genetics fault.
It is something you have to do your homework on before making a decision.