Not subscribing to plumbing magaxines just means the signal to noise ratio in them is bad.
For the value part: What if plumbers use Facebook (which they do) and when they see your FB ad, they buy your product. Wouldnt that indicate they do care about your app?
So? Maybe some ends justify the means. Selling an app isn't such an end.
Is being able to sell your stuff all you care about? Because that's the impression I'm getting. I'd summarize our discussion like this (exaggerating for effect):
> Ads damage democracy, make everyone unhappy, they're a huge drain on our economy and can be replaced by better methods of distributing information.
For the value part: What if plumbers use Facebook (which they do) and when they see your FB ad, they buy your product. Wouldnt that indicate they do care about your app?