Sounds like you have a few concerns about this guy. I would be extra careful if you are concerned.
A deposit to hold the car until you get there is definitely in order. However, it should be made clear that deposit is to be returned if something isn't right. Then again, maybe he won't be agreeable to that. You could fax or email him something written to that effect along with the deposit. In my store, a credit card is ok, but in this case, a bank check might have to be what you use.
As far as sales tax, that is paid in your state, not his, if you are shipping it. And don't let him tell you any differently! Some states (Massachusetts for one, where I am) require the buyer to pay the sales tax in MA IF he drives the car home but not if it is shipped. Even when it is paid here in MA, the buyer does not have to pay it again in his own state. He will only pay the difference if there is a difference in the sales tax rate. It's a little confusing sometimes. However, you will NOT pay him!
Elaine