How do I sell a whole set?

To sell a set as one unit, list it from My Sets rather than listing each car separately.

What happens

When you list the set for sale (or trade), the for-sale status and asking price cascade down to its member pieces automatically, so the whole set shows as available together. Two sensible exceptions: members you've pinned to a different status, and any piece already marked Sold, are left alone.

If you'd rather split it

Selling individual members instead will trigger a "break up the set" warning — see What happens when I sell just one item from a set?

For listing the fields themselves, see What do I set when I list something for sale?