Do you know where can I buy high quality container parts?
It's called bump steering, and it's caused by bad suspension. Check your ball joints, coil springs and tie rod ends. At least one of them is broken or close to breaking.
Maybe I'm missing something, but I would let it go to auction and go there and bid on it because it will be way cheaper, He just wants to sell it to someone because he knows he can get more out of it. You don't need one till harvest any way right? I would check into the auction, or just keep looking. I am sure you can do better, but I am not there so it's just my suggestion.
sounds like front end alignment or tierods need looked at. also could be bad shocks or struts. might also be a bad tire or unbalanced tire