Pinterest is a lot like Flickr and Instagram where the main draw is static media. In those places people are mostly wanting to consume creativity and are not interested in being sold to. The difference with Pinterest is people make a list of images to dream about within a project or a journey they're considering. Capitalizing on that is difficult because your best use is to simply drive traffic to a place you can convert someone. And cars for sale isn't something many Pinterest users are utilizing Pinterest for. Sure, there are comments and even communal followings where products are recommended, but rarely is the seller not also the artist.
There is a way to use it for "soft sell" purposes, but it might not be worth your time and effort in comparison to other ventures you could enhance. You can make a board that showcases the beautiful places within your marketplace and call that board "Places to visit in Mount Vernon, IA" while making sure your username or opening statement clearly identifies the dealership...."this board brought to you by Greg Motors in Mount Vernon, IA." And then you're going to sit back and wait to see if people react through the Like or Re-Pin actions Pinterest provides and call those "impressions" as a way of measuring.
I personally utilize Pinterest to help draw attention to my photography because people can click an image and land on my website where they can see a full size image and buy a print. People can digest my creativity, express their interest, and immediately make a purchase if they desire. But if you're using images of car on the front line to make boards, I wouldn't forecast great successes.
If you search for "Cars For Sale" on Pinterest you'll find a lot of special one-off vehicles with high-quality imagery. If you're an exotic store with exceptional trades and have an amazing photographer with incredible locations then you might get some action.
