You have to realize that this type of job would cost at least $2500-$3000 at a body shop. If this deal is for real and he would charge you $200 for rust removal and paint, I would make sure to get every little dent and pop it out and/or bondo it, so that when you have a fresh coat of paint, you wont go, "shit I should have patched that little spot there." This is something you can do yourself anyway and let him do the rest because Im sure tha for $200 hes not gonna sit there for 2 days and take care of every little blemish.