If you've ever played a free-to-play game like Candy Crush, Plants vs Zombies 2 or Clash of Clans and defied the "free" part by parting with your cash, don't be ashamed. I've never met anyone who actually buys items on any free-to-play, but then again I've never met anyone who's lost money in Vegas, either.
I'm not ashamed to admit yes... yes I have... bought items in free-to-play games (I've also lost money in Vegas). Trust me, I feel the appropriate amount of shame and self-loathing. But don't judge too harshly. If you haven't spent money on these games, odds are you will pretty soon.