Yes, it's not hard to have a clean carfax on a vehicle. A lot of times, information just doesn't make it to the carfax. You can also pay them to take stuff off I've heard. Not sure if there's truth to that, but I do know that you can dispute information on their and that can change the carfax.
Example: You go in for an oil change and the mileage is notated incorrectly. You then go to get a state inspection for the vehicle (we have to do these annually in MA) and the mileage is less than what is reported on the history report. The vehicle will now show for a possible "odometer rollback". The vehicle never had the odometer messed with, it's an honest mistake. Carfax can make a change to it, but there is a process.
There are also multiple different vendors that provide a "carfax". Carfax is just a brand for history reports. Other vendors have ways of adjusting the information. If you want, DM me your
VIN and I can try to see if there's something negative in your history report. We use a different brand instead of Carfax.