Virtually every business with an online presence has run retargeting ads at some point.
These are the ads that once you visit a site, they keep following you around the web, from Facebook to various other online sites.
What most businesses get wrong is that they are treating every visitor the same way. This means that regardless if you visited 1 page or 10, stayed on a page for 1 second or 5 minutes, purchased or not, you will be retargeted the same way and you will see the same ads as everyone else.