What should I do when sending a deposit?

I am planning on purchasing a car from a seller online. He needs a deposit for it before I come pick it up. What can I do to make sure that he doesn't keep my deposit and cut off contact? I'd assume some sort of contract would be needed, but how it is possible for him to sign it being multiple states away.

I'd check into an escrow company that'll hold the money until you are satisfied with the transaction. I've heard of www.escrow.com and I'm sure there are others out there.

I used www.escrow.com when I purchased my car online. You must write your own contract to be sure you get what you want. They will hold your money and not release it until you give the OK. Be sure to allow enough time in case there are delays. The contract you write will have to be agreed to by both the buyer and seller and will should contain specific performance milestones. In other words, the seller will need guarantees from you so you won't back out if you change your mind otherwise they won't have any incentive for signing it.