Fakes are not mocks. A fake is an actual implementation of the dependency that runs in-process/in-memory. This means that, unlike with mocks, your test code does not dictate the behavior/outputs.

Ideally, service owners would write and maintain the fake to ensure that it stays in sync as changes are made to the actual service.

Basically what Cyph0n said, fakes and mocks aren't the same thing.

But it isn't quite as smelly when I see a mock (or "stub" more typically) used as an expedient way to create a fake to pass in as a dependency.

Like you said, it is asserting on the interactions with a mock that is what primarily smells bad to me. I very rarely (honestly I think maybe never) see this done in a way that isn't just rewriting the implementation of the method as expectations in the test.