It's the knock that every car-buyer dreads; the news that the dream car that you have just bought from that nice man was not actually ever his to sell. And it belongs to the debt collection agency that was pursuing assets.
Or, it belongs to someone who recently had their keys robbed from their home. Worst of all, it can be impounded and if, as seems very likely, the seller has suddenly become untraceable it means that the wedge of cash that you handed them is gone for good.
So after they have taken someone else's motor for a ride, how do you prevent auto-crooks from taking you for one? There are no guaranteed safeguards, but follow our key-point guide and you can at least minimise the risk.
First, use your basic sense when you arrive to view. Is the seller an 18-year old mysteriously flogging a recent-model Mercedes? Are they meeting you at their home? Do they have a plausible reason for selling? If your gut feeling is bad, it's probably worth passing it by.
The Sherlock Holmes-approach will only get you so far of course, so look for more direct evidence.
First check should be the external vehicle identification numbers (VINs) etched onto the windscreen and side windows, which should match the engine and chassis numbers which are found on a metal plate on the engine and normally placed beneath the carpet on the right of the drivers' foot-well.
These should be pristine and flush with the mountings. If the numbers don't match then the car may have been fitted with replacement parts? Ask to see receipts.
Look for any signs of damage that could obviously be related to a theft such as signs of damage to a window or door seal or marks round the locks or bonnet. Also check around the cladding of the steering column and the ignition.
Ensure that all the keys match? Unless you are looking at a serious banger, they should and there are few plausible reasons why a car should have mis-matched keys for its ignition, doors, boot and fuel cap.
Although legitimate owners often lose them, if the vehicle has an immobiliser check that you are given the Master keys. Two sets of keys should be available: if there is just one then ask why and also be suspicious if they are not maker-branded, plastic-moulded originals.
The ultimate test has to be the paperwork. Without the original V5 logbook documentation then walk away. The usual excuse will be that the documents have been sent to the DVLA, but someone intending to sell their car is unlikely to put the most essential component for a sale in the post unless they have only just bought it.
Any car sold since 1997 will also have been issued with V5 documentation which features a green tear-off slip for the owner to keep as proof of ownership when they send off the originals.