Full-Service Marketing for Car Sales

I sell affordable used cars and, at the moment, my only online presence is the stock I list on Autotrader and Gumtree. I now want to turn that limited exposure into a steady stream of phone calls and messages from qualified buyers... (Budget: £20 - £250 GBP, Jobs: Advertising, Digital Marketing, Internet Marketing, Link Building, SEO, Social Media Marketing, Website Development, WordPress)