Obvious solution: Funding Model Tab
If the google wasn't so EVIL these days, they would solve some of these problems. Broken funding models have a rather simple and obvious approach. Just disclose some additional information that would help us in "following the money" to assess whether or not an app is legit. This is not the only way it could be done, but just one form to make the suggestion more concrete.
There could be a "Funding" tab that would describe the funding model used by the developer of the app. Most of the common options would be boilerplates that a developer could select. The most obvious options (for free apps) would probably be "Ad supported" and "Limited-function version to promote paid version". That part would be under each developer's control, and should even include free text options if the developer wants to say more.
At the bottom of the Funding tab would be Google's part, which would not be accessible to the developer. Maybe the google can't say anything, in which case it would say "We have no evidence to support the claims made in the developer's financial model above." It might say "This developer is earning advertising revenue in the top quartile of app developers" or "This developer also produces <full product name>, so please see that page to learn more about the funding."
Having offered that suggestion, I have to admit that it may not have done much good in this specific case because the financial model was pretty clear, and it was just the big lie. However, I think the reality was that the other anti-virus companies should have shot this one down quite quickly. Obviously, they should have downloaded the new competitor, and as soon as they tested it, they would have discovered it did nothing. Hmm... Now that I think about it, that's probably how this scam collapsed.
Another way it might have collapsed is if the google is checking for sock puppets, as suggested by another commenter (who I can't see now). Again, obvious, but I think the google is too EVIL to be bothered.