HPI check waste of money?

I've been reading up about these HPI checks and how they can identify whether a vehicle has a hidden past etc. From what the adverts suggest, the HPI check seems fool proof but is it really? After doing a bit of researching, a lot of opinions suggest that a HPI check in no way guarantee's a car is legit. For example, a criminal writes off their blue Ford Focus but doesn't inform the insurance for instance. They then go and steal another Ford Focus in the same colour as the one written off, put the plates from the knackered car onto the stolen one, cut the VIN stamp out and weld into the stolen car and there's now a stolen car which is running on false plates and tags. V5 documents and what not can be forged, so for unsuspecting people, a HPI check surely wouldn't provide any indication that the car you're looking at is in fact false? The reason I ask is that my father has been looking at what I think looks like a dodgy motor, the VIN plate on the floor has apparently "rotten through and had to be welded" so there's now no stamp on the chassis and it's easy enough to change the tag that's on the dashboard surely if it is a stolen car right? The car is pretty cheap hence why he's looking at it but I'd rather him not having the police seizing the car and him losing the money for it. Is there anything else I can check over to ensure the car is legit, any VIN tags in the engine bay I can check for?

HPI is not foolproof bit they do offer cover against being wrong to the person who pays for the check. If you check numbers and details properly it is very useful. They miss very few.

Nothing is foolproof, but an HPI check is definitely NOT a waste of money.