Today, the DRM-free store GOG announced a few changes to how they will handle refunds for games purchased through them.
In short you will now get 30 days to refund a title from GOG, which includes games currently in development which previously only gave you two weeks. Even if you've downloaded it and played it, GOG say if it's within 30 days of asking they will give you a refund.
A good policy, 30 days is a pretty good amount of time to refund a game. However, it can be open to abuse of course. Sounds like they will keep an eye on people doing it often though, as they said "we reserve the right to refuse refunds in individual cases".
With how they're handling them now, this might actually be the most consumer-friendly refund practice for an online store. From looking it over it definitely seems better than Steam, Humble and itch in terms of how friendly it's presented. Steam is locked down to two hours playtime and two weeks, Humble Store don't give a timeline on it but they do accept refunds of course (they've refunded me personally multiple times), itch.io also don't state if there's a particular amount of time, Epic Game Store is the same as Steam and Origin is also two weeks and without playing any.