In AppStore and Google Pay aswell as on Facebook there are lots of games you can play on your mobile for free. At least they are free when you start playing them.
After a while you get frustrated since it takes too long for you to grow your city, character or whatever the game is about. Then it is easy to pick any of the “offers” the game company offers to you in order to develop faster.
This is a clever trick to hide the fact that your free game actually is more of a pay to play game. Ok, yes you are still stuck on level 7 after three weeks of playing, but if you buy this bucket of goodies for 4.99 Euros (or USD or GBP) you not only get automatically promoted to level 10, you also get a shiny but pointless badge that don’t improve the game in any way. And after three more weeks you realise you have spent close to 50 Euros (or USD or GBP) on a game you thought was free.