Okay, I will start a useful but short guide for the bug you get when you are trying to /sellcar and it appear ' You don't own any vehicles '.

You got 1 empty car slot in your /stats and you can't sell your car you got in 2nd slot because you always get the bug stated above. So the solution to this is very simple: Go to Jefferson Dealership, Buy Faggio so your second car slot can be filled, then /sellcar to the buyer and the bug will not appear after you got your second car slot filled, If you want to keep the faggio keep it otherwise /sellcartomarket then /sellcartomarket confirm.

ENJOY

Sincerely;
Alexander Tylor