They are an opportunity to offload a piece of rubbish which would otherwise be unsaleable.
I dumped a massively faulty, though not unsafe, car on the most famous of these outlets a couple of years back, exploiting the inability of the commission-driven, largely untrained, staff to identify faults deeper than the cosmetic.
After submitting the vehicle, I quaked for a few days, as the company allowed itself 4 days - days in the absolute, not working days - to 'inspect' the car, but the agreed sum was paid to my account without problems. I got round most of the 4-day provision by taking the car round for its initial assessment in the dying minutes of the Friday before a Bank Holiday weekend.
Fraser