I know a game designer who does this semi-professionally. He really spends a long time in the alpha and beta testing phase of game design with lots of playtest

I know a game designer who does this semi-professionally. He really spends a long time in the alpha and beta testing phase of game design with lots of playtesting in different groups. He recently launched an amazingly fun social deduction game on Kickstarter called "Feed the Kraken" with tons of gameplay elements previously unseen in social deduction games. I think that professional designers often have a hard time competing with the amount of time invested by these enthusiasts.