Doc, I just did a search on digital mileage correction on google and I am really really shocked

I didn't know that it was so easy to clock a digital odometer... I am planning to buy a Mk4 Golf GTI Anniversary for my wife - or a Lupo GTI

- but how would I tell that some sneaky t055er hasn't clocked the car using one of these services? Is it traceable ? Especially with a fairly new car - I mean I could do 40k on my Mk5 GTI in a year and reset everything to around 18k.. how can people tell?