Personally, I'd release free demos, to get people to play your game, while people will buy your game is they've got no idea who you are, however the odds are much much lower. Have people play a demo for free will make it easier for people to know and play your game, making it easier and the higher chance for people to buy your game once you fullly release it.
Anyways that's what I'm doing.
The only sites I know that you can sell your game is itch and steam. But steam has a pretty high fee.