When I look at a second hand car I always have a quick eyeball at the discs. If they look scored and worn I factor that into my budget. If you are lucky, as I was with a Polo with 60k on the clock, they had all just been done all round.

It’s a second hand car with nearly 40k miles . Brakes wear out as you drive it. Minimum requirement for mot is 1.5 mm brake pad thickness. Discs need to be severely warped , cracked or corroded or reached their minimum thickness before replacement. If the car passed the brake roller test on the mot , then there’s not much wrong with them .

Thats the theory.

In practice my cars in Scotland ALWAYS failed MOT for visible rust on the disks, though they passed the brake function test just fine.

Fortunately on most cars changing the brake disks is fairly easy (though not on the hub-over-disk AKA captive rotor designs used on, for example, 90's Honda Accords and on my last car, a Daihatsu Skywing) so I was able to keep a shiny set of disks just for my Renault 5 MOT's.

If you do it often they dont get rusted very firmly in place.

More recently, power abrading with flattened beer can seems to be pretty good at cleaning them up, though I'll probably never have an opportunity to test that against the UK MOT.

New cars don't get mot til 4 years now, this would have been picked up if mot at 3 years