both shows are for selling things useless, or unused in the houses to gather money for some specific reason, such as a new bed, a holiday, a more charity type thing, or new hobby etc.
The difference is that car booty is based on more on rubbage that people have lying around, within lower income families, and the cash in the attic, which the two shows are shown back to back in late mornings in bbc, is more on real antiques, more than 100 years old things collectables.
Car booty sells things in a car booty sale, while as cash in the attic sells things in auctions. Car booty earns such as 200 to 500 pounds, while as the cash in the attic goes for 600 1000 pounds.
Another show which takes the two together is where the participants the red and blue team, goes and buy something at the car booty and then sells it, hopefully for a higher price at an auction!
Is this a representation of the segregation of class that is embedded in British societies? Maybe.