Thats a good point, i would certainly be put off if a car i was looking at had an engine replaced. They never seem to drive as well. Although, if Nissan put a really good engine back in with a lot of care and attention, then it shouldn't really be a problem. Also, full documentation from nissan, explaining the reasons behind the swap, and the current mileage of the new engine, with proof, may even help the resale of a higher mileage car.