thats absolutely correct. Many cars sell slow if their meters are not tempered with. Trust me, I am experiencing the problem myself as I have not tempered my car's odo. I do have the resources but I will never do so.
One should use some common sense and compare the reading with car's physical condition. Check interior, exterior, suspension and drive of the car. It does tell lot of things.
high tech cars have a lot of back ups and their original odometer reading can always be checked even if you temper it.
on the other hand, technology has made things a lot more easy. Thanks to China.
There are instruments available now with which you can reprogram the ECU to reverse the odo. Options are available for BMW, Benz, Audi and Porsche even let alone Toyota and Honda.