Steam is quite generous about refunding games, either because you purchased them accidentally or they didn't run correctly or any other reason, as long as you don't have more than a few hours in the game. I think that's a much better approach than having to implement what's effectively a DRM system in software, or a completely separate trial binary containing only part of the game.

> as long as you don't have more than a few hours in the game.

Last I checked the limit was the minimum of "2 hours playtime" and "2 weeks after purchase"

> Steam is quite generous about refunding games, either because you purchased them accidentally or they didn't run correctly or any other reason,

Again, last I read, Steam is quite generous but will probably flag your account if certain patterns emerge (probably through some ML-alchemy).