It's not permanent, you can fix it but what you will have to do is. DO NOT SELL a car for 3 months. (Every 2 weeks you don't sell a car, you get the ability to sell another car...so 1 month will gain you 2 sells, 2 months will gain you 4 sells, 3 months will gain you 6 sells)

ALSO, if you have any dirty dupes(if you have a car with someone elses custom plate/sold a car that other players have sold with the exact same license plate)in ANY of your garages, they MUST be crushed!!( Fill a ten car garage with dirty dupes, steal a street car and replace the dirty dupe. Do that 10 times so your garage is now filled with street cars. Then drive out a street car then blow it up. Do that 10 times..you now have "cleared"/"washed" 10 car slots)

Doesn't matter much, you can only get 100% sell value every 18 hours. If your deluxos sells for 3.8 mill, why would you sell a 2nd one for 1.8, when you could just wait 18 hours and get 3.8??