The simple answer to this question is well.. you don't. That's why you test it and keep testing until you find something that really truly works for your dealership. Once you find something that is working you can then dump money into it. If you are really worried about if it will work you can do market research on competitors or things that have worked for others.
This is something we do typically when we are breaking into a new market and wanna work off of something that has already worked. It's ok to build off of someone else's testing and money but you still will never know for sure 100%. If anyone tells you that they can tell you 100% that it will work kick them out of the room because they are lying straight to your face.
Hopefully this was helpfully to you and you take a few of these things and use them in your business to help you get results fast and consistently. Follow the formula we shared and you will have success.