In most states or at least mine in the Usa tampering with a speedo is a felony however the laws are dim once a car is 20 years old there is a piece of paper that is a as is buyer agreement that exempts seller from such things as a speedo reset when the buyer signs it maby someone found the original motor and figured it had 30 k miles on it and reset the speedo
but that would still not be right I dont agree with that kind of stuff but thats just my opinion