Mori_Yuki: While very possible I don't think that that's a good idea. Usually you can return a game within 30 days and there will be no questions asked. You can also play a game as long as you wish to because there is no time-limit of 2 hours like Steam has it. If it's a one time thing, or you do it some months apart and keep other games you bought, no one will have a problem with this.
When you are asking for refunds within a very short amount of time, or if you have bought a bunch of games and now wish to return them all because you used them as a demo, GOG might get very suspicious and it may have negative consequences. Once there is a reasonable suspicion of abuse, they might not grant your request or even block you from filing one in the future.
The best method when there really is no demo is to watch Let's Plays and reading reviews and then decide whether you should spend money on it. You can also keep an eye out on Steam where usually there are demos for many games. During a demo festival or from the developer itself - both for a short time only so you have to be quick to get access to them. Doing this to be able to make an informed decision is of course no guarantee that you will like it. When that happens you can safely ask for a refund every once in a while.
I agree, it's important to be mindful of how and when you request refunds for digital games. While some platforms like GOG have more lenient refund policies, repeatedly returning games shortly after purchase or abusing the system may lead to consequences.
To make informed purchasing decisions, it's a good idea to rely on Let's Plays, reviews, and demos when available. Steam often provides demos, and taking advantage of those opportunities can help you avoid unnecessary
refunds. However, it's also important to understand that even with research, there's no guarantee you'll enjoy a game. In such cases, requesting a refund occasionally is a reasonable course of action.