[dillondoyle]

There are plenty of examlpes on both sides.

I have routinely gotten over 100% immediate last-click roi from fb ads, for many clients.

I know for a fact many others have too. There are a ton of direct to consumer online-only products that easily measure this. Just make a page or item which you only use to advertise on FB. sales/spend. Game developers track this closely too.

[runarberg]

This is anecdotal evidence. Nobody is disputing those exists. However I think FB and Google owe their existence a little better evidence, such as A/B testing, control group studies and even experiments to actually demonstrate their effectiveness. Until we have those (and perhaps we do; I seriously know nothing of the existing literature) the anecdotal evidence we do have should be taken only as indicative of effect, not proof of effect. Anecdotal evidence come with a ton of bias.