You'll find your horse, if you listen to your heart. If the seller is neat, clean and takes some pride in himself and his facility, then he probably cares for his horses in much the same manner. Ask to see the horse in his stall or pen. Wood chewers and cribbers leave tell-tale signs. So do weavers and hole diggers.
Bad habits are physically hard on a horse's condition and health, and they are always hard to break.
You don't want those problems. Ask to see the horse turned out so he can run free and you can see how he moves and uses his body. The horse should be happy to see people, curious, but not jumpy. He should have a clear, bright eye and should be smoothly put together. The horse's conformation should be pleasing to you.