I used to work an ad tech startup (we ran ads on Facebook, Google, etc.) and we could easily track conversions led through our ads on Facebook. Websites instal

I used to work an ad tech startup (we ran ads on Facebook, Google, etc.) and we could easily track conversions led through our ads on Facebook. Websites install a "Facebook Pixel" which helps track users through ads and sites, and there is a lot of tracking data from Facebook through to a conversion, whatever you define that as. This was roughly 2 years ago, but we had extreme clarity to how well ads were doing and how much it cost to get a conversion of someone by an ad. This could be defined as someone buying something, so you could get "it cost $x to earn $y" pretty readily.