Trilarion: For that I really like the Steam way of having a two hour testing period. And if I understand you correctly that's exactly what you want. After all the best demo for a product is ... ... the product itself. So if Steam is an option for you I would try that out.
Well, those two hours are definitely good, made use of refund system in two cases and everything worked great. As an idea, one game was Rust. It's an early access game. These are the specs:
OS: Windows 7 64bit
Processor: 2 ghz
Memory: 8 GB RAM
DirectX: Version 9.0
Storage: 8 GB available space
I meet all the requirements, but guess what, game it's unplayable, as i don't have such a good card. I'm not talking like "well, it run at 20 fps, not fancy enough". I waited around 30 minutes for it to load the world and i got errors two times. Basically, one from these two hours were wasted in loading screen. Then, in game, i was really getting something like 2-3 FPS. I would think that minimum specs would be in order for that game to be playable, not in order for that game to run. 2-3 FPS it's not playable.
And that's a happy case, as i got the game in order to play it with some friends, so i tried it right after i got it. But i have many games that i bought on sale and i didn't got into playing them in those 2 weeks. Not to mention that not all sites offer refund periods.
Alan Wake it's another example. There i meet the "Recommended" settings. But game moves pretty bad on low settings. Not as bad as Rust, but bad enough in order to be unplayable and annoying.
As consumer, i feel robed by buying something based on specs and not being able to enjoy it. That's the difference when you buy physical products too. If product it's faulty due to factory errors, at purchase, you are entitled to get your refund. But if the product does not have manufacturing problems, but it does not work as intended from different problems, you have the seller guarantee and you can apply it on that product. And the seller it's obliged to offer you enough information regarding the usage of the product.
In case of games, these last part of what i said earlier it's often ignored, as i'm not receiving correct information about the product that i'm buying. Minimum specs might mean that the game will run, but if i'm not able to enjoy it, what it's the point in order for me to want that product?