Could be a variation of an old scam.

Let's say you ask $5000 for the car.

Then they send you a check for, say, $9500 "by mistake."

That's OK, they say, just deposit it and send us a check for the difference.

So you do.

Needless to say, your check is very good and their check is found after 2 weeks to be very bad (that international time lag's a bitch).

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If you decide to go along, deposit their check and wait 4-6 weeks TO BE SURE that their check won't eventually bounce.

If I were in your shoes, I'd discuss with my bank manager the best way to CONFIRM payment from the UK before releasing the car (e.g., through the US branch of the buyer's British bank).

And never send them money.
--
Don Foster (near Cape Cod, MA)