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But this is how online advertising works.

AcmeShop can equally run ads on other companies 3D printers on Facebook.

And they can equally run ads on Google about Facebook Marketplace.

"Normal" online advertising is neutral with respect to companies bidding on placements. Not so much with Facebook, which is under no obligation to run a bid on every ad they serve. Some of those ads are dedicated Marketplace ads, and AcmeShop can't bid on them, or even limit access to the data that Facebook collected while performing their contractual duties to AcmeShop.

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