This might be an unpopular oppinion, but I think MSFT shouldn't have a say in what developers can charge for their efforts. That's why it went through the checks: If the developer thinks his efforts are worth $500 per app install he should be allowed to charge that much. And I, as a customer, should be allowed to not buy it if I don't like it. Let the market decide what sells and what doesn't
If I decide to make an app that allows you to have a tile on your screen that says "i paid $800 for this app", I should be allowed to do that, as long as I clearly state that this is all it does (i.e. I do not do false advertising telling you it'll do stuff that it actually wont.)
But you should also not forget that there can be valid reasons for such a high price tag. The price could include services, licenses, fees or subscriptions.
Far more importantly, I think there should be a proper return policy for apps on the marketplace that would allow customers to return a unwanted paid app (accidentally paid, false advertisement etc.) in a reasonable time frame (not the useless 15 Minutes of the playstore but a few hours if not a full day!)