"First time buyer only" mortgages - How would they know?

[Goochie]

A colleague lost his old job a couple of years ago and had to move back in with his parents. He was lucky enough to be able to sell his house before getting into difficulties and is now back in employment.

He has been looking at mortgages but the best deals seem to be for "first time buyers only" - I said to him, how on earth will they know that you've had a house and mortgage before?