GOG.com is filled with games that defined my childhood, and even part of my adulthood, and is now offering a new Worldwide Money Back Guarantee. So, for whatever reason a game doesn't work on your PC, you'll get a full refund.
GOG.com admits that a game not working is a rare occurrence, but at least if it happens, you know you're covered. All you'll need to do is fill in a ticket and allow GOG's "top men" to research any potential fixes for the game. If GOG's goons can't find a fix, you'll receive a full refund, as long as its within 30 days of your purchase.
It doesn't stop there, with the site also offering "accidental" purchase returns - in the case that you already own the game, and purchased it again. You have 14 days to return your game if this happens to you, but you won't be able to try before you buy - if you play it, the game is yours.