I.ve imported a car from U.S last year, and will soon get another one. What you must have is the title (pink slip) and a bill of sale stating the price you've paid. These are very important as customs needs to see them for evaluation. Ive bought car from private persons, no problem.
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Most brandrelated sites, as this ford forum, has a sales forum.
Some sellers are biased to sell to foreigners from outside U.S for some reasons, and asks for references. I've never bought anything from people who can't accept my cash money without asking for references.
For freight use a broker who can assist you all the way to home.
Good luck.
