There's one car in particular that's for sale here in Canada which I won't mention publicly because I don't want the dealer trying to sue me. Basically what happen was an authorized dealer purchased this car sight unseen, this was during the crazy market back in Feb when dealers had no inventory. Upon inspection they found out the car, which is a few years old, had almost 15,000 more miles than what was shown on the ODO. The dealer basically had to order a new cluster, enter the correct mileage and wholesale the car.
Moral of the story, there's a lot of roll backs out there and it's fairly easy to put mileage blockers on our cars. Another thing I would look for in a Carfax report is if the car is getting serviced at a 3rd party garage even though the car has warranty. The reason for this is the owner is trying to keep the car away from an authorized dealer so they can't find out there's a roll back or enter the correct mileage and screw up the Carfax report.