Take another horse knowledgeable person with you. Take pictures. Take a video. Take pics of her teeth. Take pics of her feet.
You can ask whatever questions you like, but you may not get accurate answers. Sometimes people don't know, sometimes people won't tell.
What do you want to do with this horse? If she's going to be a pet, that's fine. Anything else, you need to get those x-rays, line up a good farrier/trimmer and vet and sit down with them for a discussion.
How long have they had her? What are her two worst training/behavior faults? If they say she doesn't have any, don't believe it. Can they show you vet bills for the past 2 years?
Other questions depend on what you want to do with her. If she is able to be ground worked, then do so, but if she is currently in pain, then she will have difficulty. I doubt you can ride her.
After you see her, come back to us and let's see what we've got. I took in a lame mare about 7 years ago. I wanted her to be a companion to my other horse. The other horse is now gone, as are two others since. The "lame companion" came out sound and is the only horse I now have. I ride her all the time and am going in an endurance ride this fall with her. So you just never know.