I heard quite a lot about this stupid practice and wondered about this, as a BMW mechanic assured me that is difficult to clock a BMW (E30's included) as if you do so a tiny red led would appear in the mileage clock. Also apparently the dealers have another way of knowing the mileage by measuring the engine, not sure which part or how, I believe by analysing the wear as such or something to do with the pistons and cilynders.
Perhaps by changing the speedo cluster that would be a job done, but how easy is to cheat and sell us a turd ???
It would be interesting to know ways of checking exactly how honest a mileage meter is in our cars/potential buys ?
Jose