If he's serious about buying the car, I would demand a much bigger deposit. You don't want him changing his mind, or finding a different/better deal before he closes with you.
One thing you can do is see if a local bank could hold the title and funds in escrow until the final amount is deposited. But whatever you decide to do, make sure it is CLEARLY spelled out, in detail, in a "bill of sale" signed by both parties.
Years ago I sold a 240Z, and the kid that bought paid all but the final $500 up front. I agreed to give him a loan for the final $500, payable $100/month. After 2 months, he totaled the car. I had to chase after him for several months to get the last of my money; he had a hard time understanding why he still owed anything if he didn't have the car anymore
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