Reminds me of a website that used a random number generator for the "<n> persons are looking at this right now". The random number would be stored in Redis for some time so it wouldn't go randomly up and down upon refresh, at which point it would be obviously fake.
Candy Crush Soda Saga does it with microtransactions.
The game is a puzzle in which you need to do something in a limited number of moves and on defeat screens there are notices along the lines of "420455 people bought extra moves to beat this level".
