years ago, the dollar amounts werent that large even. my game company bought us all gift cards and told us all to each buy a couple hundred dollars in our app to bump a couple spots.
another interesting thing, basically everyone on the top grossing chart knows roughly what the others are making - as you adjust ad spend you adjust your revenue, and when you pass someone you know how much they are making. (or just through word of mouth or multiple games)
even more crazy was buying tens or hundreds of thousands of downloads to get to the top of the free charts from bots, before apple claimed to be cracking down, which then triggered a couple percent of that in legitimate downloads. those 'organic' downloads from the charts ended up costing a fraction of what paid ads would have cost if you average the bot download cost over them. then marketing/coo lying about not using bots......dont know why they thinks they can hide stuff from the engineers