CarFax reports ONLY the information that is reported to them. If you run in to a tree, and repair it yourself, the CarFax will not know about it. The same goes for owner maintenance, although most dealer maintenance is not reported either unless it was something major. If you have no state inspections, then yearly mileage is unknown. If it had flood damage but no insurance claim, CarFax does not know about it. I think the salesman was being straight with you and even with automobiles, CarFax is limited on it's usefulness.