There's a thread already about this. It's 10, 8, 6, 5, 4, 3, 3 for 4 months and 3 for 4 more months. Hitting sell limit doesn't affect your next day limit. Only selling 3 cars within 12 minutes.
you are wrong, the original limit is 30 and when you hit that the next day you can only sell 12. the 10, 8, 6..... is only once you have built the limit back up again. when i hit my 30 the first time i was selling a car every 10 mins and it still dropped down to 12 the next day. and i had built mine back up to 10 a day then tried to sell 11 and that put me down to 8, so i then started hitting limits all the way back down to 3. i have been closely monitoring the behavior of the limit since the sultan MC dupe months ago. so until you can provide me proof that i am wrong i am going to continue my research.
and there are loads of threads about this. most of them are unconfirmed as people think they have worked their limit back up but in reality it has been a tuneable alteration and a coincidence, what makes me laugh is these people have gone and reduced their limit back down again because they thought they have it solved.