> Why would FB ever tell me to spend less?

There's literally a team at Facebook (Marketing Science), part of who's job is to tell advertisers what actually works and often, this can lead to them telling advertisers to spend less.

And this is an incredibly smart business strategy in that FB know (from experiments et al) that their platform works, and if they can show incrementality, then advertisers will invest more in the platform.

In game theory terms, it's a good strategy for a repeated game, which advertising definitely is.

It's fair to question credibility, but you have to realize that their results can be compared against 3rd parties, and it would lead to a lot of reputational damage (and also legal risk) to systematically defraud your advertisers. All it takes is one smart team to out the entire enterprise.

The causal incrementality of ad spend is rarely negative. You expect to see decreasing returns with additional ad spend. For each dollar in ad spend, one advertiser might want to see $3 in revenue, another $5. Incrementality studies then allow advertisers to tune spend to their operating points.

Facebook does like money. Do you think lying to the biggest advertisers in the world is the best long-term strategy, or do you think instead it might be better to report out the most accurate results possible?

Facebook has a history of screwing advertisers ("want your page to show up in people's feeds? Get more follows, here's how to buy ads targeting that", then one year later "we've decided to downgrade pages in people's feeds"...), bankers (their IPO pricing), and essentially everyone they have a business relationship with. I'd expect them to stretch the truth as far as they can get away with.

Most accurate results possible you say? https://www.latimes.com/business/story/2019-10-10/hiltzik-fa...

Long-term strategy? https://www.businessinsider.com/facebook-allowed-fraud-hacke...