There are so many variables in this.... it's really a case by case basis. A BIG question for me is (and I'm assuming bad xrays), how bad is it progressing? I know horses that have questionable xrays from 5 or even 7 years ago that haven't changed at all. If they are serviceably sound and not progressing, I wouldn't be as worried. Now if a horse's xrays have changed considerably in just a year or two, no, I'll generally pass. Although... One of my students tried a $35,000 horse that was a perfect match, everything that we were looking for, great flexions, but had terrible xrays. Like, going fine today but could fall apart tomorrow... they went ahead and bought him for $4000. The thing is there's no way we could even find a lease for close to $4000 for the quality of this horse so they took a chance. He is a ticking time bomb really but she's been showing him for the past 3 years with no issues so I'd still say she lucked out. Your budget will be a big factor in how big of a risk you can take. And how many years you think the horse might be able to do its job. And if you have a plan for the future of this horse if you need to retire him.