The FAQ states
Questions related to the maintenance and repair of motor vehicles and
their accessories, internal combustion engines, even in applications
other than automotive so long as the question is related to engine or
It doesn't seem to fit based on that statement, but the community defines the scope of the site, and that statement isn't meant to be all inclusive.
The FAQ goes on to say
You should only ask practical, answerable questions based on actual
problems that you face. Chatty, open-ended questions diminish the
usefulness of our site and push other questions off the front page.
I think this is an actual problem you face, but it could easily be an open ended question.
A lot of automotive technicians work for shops that sell cars new and used and many are knowledgeable about the sales/trade-in process. Many automotive technicians and DIYers alike are passionate about cars and end up going through the buy/sell process a lot, and should have knowledge to share on the subject. I don't think it would run them off, or diminish the usefulness of the site by having this type of question.
So with all that being said I would say it depends on the question.
Asking a question about the specific process would be okay. How do I know what my car is worth? Can I sell it to a dealer or at an auction? How do I sell it as a private sale? Should I get a technician to check it out and disclose that information to the seller?
Asking what's the best way to sell my car, wouldn't be a good question.
But that's just my opinion, I could be wrong. Ultimately the community decides buy discussing and voting on meta.
Just a note for new users voting on meta works a little different than the main site you up-vote an answer you agree with, down-vote ones you do not.