Honestly, I think nearly everyone who's posted misread the OP's message... Allow me to reinterpret how I read this?
I believe in traing a horse with natural horsemanship but you can never trust what some people have done with a horse. I am experienced with horses and use natural horsemanship, and unfortunately there are a lof of people that screw it up.
I bought a mare not to long ago and the owner said she had been taught with natural horsemanship and was well trained but when I rode her, she had no brakes and would try to take off with me.I looked at a mare and was able to determine, from my experience, that the owner didn't do what he'd been claiming to do. There was a large discrepancy between what the owner said and how the horse behaved. However, even with these issues, I decided to buy her anyway.
It also took me an hour just to get her ready to ride, she was horrifide of the saddle and the bridle. She is also horrifide of water and people. When we bought her she had scars all over her body and she was so skinny.Not only did the owner fail at using natural horsemanship properly, but really screwed this horse up. I had to work with her a lot to fix her issues and had the experience to do so.
I don't blame natural horsemanship at all but think twice about the horses education and be weary for the first ride, just in case the horse isn't as well educated as the owner thinks. So, just as an example, though an owner may SAY the horse was trained to a certain level or in a certain way, you can't always believe what an owner says. In some cases, this may not be because the owner may not be aware of (or choose to lie about) what they have (or haven't) actually achieved with the horse.
Ultimately, everyone else posting is all saying the same thing as the OP: Don't take an owner at their word - make sure you check the horse out yourself. As many have said, failing to do so is a pretty novice mistake - though, credit to the OP, it's not uncommon for a novice to buy a horse trusting what the seller says. Trust me, I know a lot of parents that go get horse lessons for their kid and buy whatever horse a seller says is a good fit, not realizing how much trouble they're getting themselves into. However, most of those people aren't going to be on this forum. Oh well, it can't hurt to throw caution to the wind for others anyway!