Thanx for all the answers guys, ive gone ahead with the car, its been hpi check n all clear apart from the mileage which does not tally up with car but its a different engine, so makes no difference, he's gave me a 3 month warrenty and a guarrantee in writing and signed that the car has the x3 20,000 mile engine, also he givin me the reg from the x3 to check on dvla to verify mileage im also gonna ring bmw with the engine number to double check it came from the x3, if all is good I think ive gettin a decent car for price!