Watering down the definition of 'trusted' is an underappreciated attack surface and semioticians will probably enjoy seeing what countermeasures arise, if any.

You to ask: Trusted by who.

The reason why ads aren't already served like this is the risk of fraud. The publisher can just make up claims of millions of impressions with no way to disprove it.

I assume Trusted Server comes with some mechanism to prevent this. That's what the name means: The server is trusted by the advertisers.