Marketing strategy for car broker

Hi, I need an advice on marketing strategy for car broker. I work for company which sell new cars with 20-30% discount, mostly premium makes like: BMW, Audi etc. Target audience would be managers, professionals, business owners, 25+ YO basically anyone who earns well in Poland (I don't think that country is going to do any difference). I tried cold calling people who sold used cars on classified ad websites but it was like 5% of interested people. Do you have any advice/idea how to gain customers with little to no money to spend on ads?

Sorry if I posted in wrong category.

Longtail Keyword SEO is probably the easiest way. Lower competition and more targeted. You can even add the geographic location to the anchor to target it more to the area.