Big spenders do a lot of due diligence to make sure that the money they spend is actually giving them a positive return. It's not like businesses just throw millions down the drain and hope it gives them results. Facebook is working great for them and it is not a scam otherwise businesses wouldn't be spending billions on advertising there every quarter.
Or, as pointed out in a comment above, everybody is lying to everybody and the only loser is the customer. The customer may still find advertising to be a net win, but they have no clue to what degree it is such.
