Bad legs/feet. Anything more than very minor deviations in leg straightness, inadequate bone or improper foot size/shape, I am out.
I am feeding a (lame) bad-legged horse for the rest of his life and learned my lesson from him. He is crooked, straight, and has bad hooves. He’s a good horse, but…yeah, he’s been unsound for a while.
I didn’t buy a yearling last year that I desperately wanted (had the breeding, movement and conformation) as, when I went to see/buy the horse, I found that in person, the lower front leg was more crooked than photos/video showed. The yearling’s dam was on site and they let me look at her, too. She had the exact same bad leg, and, I learned when I asked, became a broodmare at 3 years old when she went lame. So I said no, and drove home with an empty trailer.
I still think about that yearling all the time, though - I wanted it SO badly! And of course there are many sound performance horses who are crooked – but I just couldn’t afford to take that risk.