I see many gas stations and mechanics offer to reverse the odometer of the car for 50 LE

why they do that?

it is not right even if they want to make money but it is stealing and it is wrong

how can you find out if the used car you are buying the odometer of it has not been reversed

i know people take the car to the dealer and let them check the vin in the computer but what about older cars

is there a way to find out or not