Selling your car used to be a no-brainer. Park the old junker at the end of the driveway facing out, stick a “for sale” sign on the dashboard and wait for the right buyer to happen by. If you’re really ambitious, you could paint the price on the windshield in white shoe polish, along with the ever-tempting “OBO.” But in today’s used-car market, the old tactics won’t get you very far. Savvy buyers and sellers have access to a myriad of online tools designed to make automotive transactions easier, faster and safer. Without a clear strategy, sellers can be left in the dust.