Trust CarFax 100%? Possible odometer rollback

[AndyP]

In a process of buying an used car, I checked out the car several times, it runs smooth and engine sounds good. Got the engine checked by a mechanic briefly, and mechanic says engine seems to be in a solid condition.

However, I check carfax record and it suggests a possible odometer rollback. Record shows that the kilometer has dropped from 300,000KM to 100,000KM right before a previous transfer of ownership was made.

The car has an original engine, and operates well. Digital odometer shows 139,000 KM as of right now.. which seems to be a normal rate considering everything. Mechanic said car is in a good condition.

Am I to trust Carfax's record 100%, or do I take it with a grain of salt if a random mechanic gives an OK after running a variety of test? Thanks.. very confused.