Suggestions…should I?

I am looking at buying a car in the US. I cannot go down and see the car until 4 weeks from now but it does look I will probally buy it.
THe guy wants a deposit which he says he will return should I pass on the car.

Is there any way I can protect myself to ensure I wll get the money back if the deal falls through?

I think I have read here if the money is sent by postal service I have legal means to have it returned???

Suggestions??