Promotion

Some of the ways a small automotive dealer like me sell more cars online effectively are:
AutoTrader.com

Cars.com

Both the above are  expensive.

AllTheRides.com is free.

They publish my entire inventory and offer a flat monthly low fee that allows me to be in control. It is free to list your inventory but if you want to take advantage of some of the premium services they offer, you can get them for a low monthly fee.