It does seem to happen, the company I work for sold a BMW 3 series two & half years old with 66k miles traded in for an new Audi.
The Audi dealer then moved the BMW on to others like they do with trade ins no fault on the Audi dealer.
A few years later trading standards asked us if we had any history on the car as we were registered 1st keepers. I keep all the service records & gave them the info we had on the car, by then nearly six years old had first mot at 31k & wasn't even up to the mileage we sold it at 3 years earlier.
The owner had had an serious mech issue & took the car into BMW dealer to fix, they flagged up the discrepancies, they had access to the service times etc all altered before 1st MOT, the car was close to 100k actual miles :evil:
was done by a used car dealer in Yorkshire.
We have also had this with hi mileage company vans as well, I would say there's a lot more to gain on a 911