Sorry if this has already been suggested:
Option to set price of game negative, to pay people to playtest.
I really don’t think that’s a good idea.
What if someone puts their game as -0.50$ and accidentally put it live, and suddenly a million users download it. Will they go 500.000$ in debt?
What if someone downloads your game but doesn’t give you any feedback at all, just for the money?
If you are prepared to pay for playtest, it’s better to find specific playtesters, pay them individually and give them a copy of your project for free on Itch. There’s probably some site dedicated to it, but I’m not really familiar with any.
I guess what you could do would be to add a section in your description where you offer a dollar or two via [service X] for mails including insightful and/or constructive feedback.
They would have to trust you, but it would also give players who already like your game an opportunity to refuse getting paid for their input, making them more motivated to write something. Everybody likes feeling charitable - especially if they don’t actually have to spend money. ;)
The main downsides to that solution would be: Having to do the transactions manually and dealing with spammers. But the latter could happen in basically any scenario, as Dark Dimension already illustrated.