ROI from adverts is always a shitshow though. If you come off a plane and see and buy it, is it because you just saw an advert for it, or were you always going to buy it. There is of course stats that may show number of impressions vs. total purchases trend, but its still just massive correlation that I imagine there is a bunch of people pulling spreadsheets together to justify their marketing spend. Anecdotally, I've heard of data teams working with marketing teams and just going "whelp, whatever you need to justify your job", etc.

Real ROI via direct sales though, that's somewhat measurable since you have a direct cost of acquisition (sales person salary, overheads, etc) vs revenue.