The £10 Goldmember fee allows you to sell 4 cars, this isnt the fee to sell 4 cars.
Basically the 4 car rule is in place to protect our paying traders, as a Goldmember you are entitled to sell 4 cars on the site every 12 months, any more than this we feel would be unfair to the traders on here who pay a much higher monthly fee for the priviledge!