Both are is an incredible social platforms for learning about your current and future customers. That being said, the worst use of Facebook as a car salesperson is to talk about specials, rates, and promotions. If you put these online too frequently, people will unfollow you. I'd never directly promote my dealership or my provider on the personal profile page. Getting your page on local business listings promoted or hiring a professional SMM company might help more I think in developing and maintaining strong client relationships, while personal use of Facebook or Twitter is just the fastest way to attract ready-to-visit prospects and convert them in to recurring car buyers.