Ultimately, the decision is yours but remember this: You have to pay for not only the horse but the equipment, agistment, feed and many other expenses as a horse owner, don't chase good money after bad. Don't be afraid to keep looking!
This horse sounds like he requires a lot of additional riding before he is reliable, and you have to decide if you want to do that or not. Or, he may need vet attention as some of the others pointed out. There will be another horse out there for you that is ready to go and you won't have to worry about your own safety!
An old trainer that I used to work for had this saying:
"If it walks like and duck and quacks like a duck; it's probably a duck"
Meaning, if he is misbehaving regularly, he needs some serious training and that's all there is to it! (regardless of what the previous owner may tell you!).