“That's the closest thing I can find to a "confirmation" that AppGratis was accepting cash in exchange for a higher rank in their app.”
For what it’s worth, in a previous HN thread, several users reported having received offers from AppGratis:
“We were told $3 per install or $100k flat rate for 1 day.”[1]
“I was also quoted a flat fee of $100k”[2]