While there is a lot of fraud, if you actually track from ad click to sale, you'll see SOME amount of results.

In most cases they will be underwhelming, but if the numbers make sense, why not?

example: 2$ per click for a $500 dollar product (assume no other costs_

if you can turn 1 out of 100 clicks into a sale, then it might still be worth it, despite 99 fake, uninterested, botted, clickfarmed or otherwise undesirable clicks.