I had emails like that when selling one of my old cars, and when selling my Gamecube.
"my agent will give you cheque and then you can send it over"
then most likely the cheque bounces or is cancelled, they have the item and the money.
I'll never sell a car to someone with Paypal or with a cheque unless they are happy to wait for the funds to clear before they get it.
Cash is best, but it could be fake notes. The best bet (if you're really suspicious) is to take the buyer to a bank, and either get him to withdraw the whole amount over the counter or from the machine, or as I did once, take him to your bank and pay in the cash he gave you to your account. If the cashier accepts it and it goes into your account, then all is in the clear.
Personally, I'd only sell to a non-UK buyer if they were willing to come and collect the car.