Yes it would leave a bad impression.

If a game were to suddenly nag me for money to continue playing, I'd instantly drop it.

If I'm playing a demo, I want to know it up-front, so the best thing to do is to offer a demo.

Yeah, the concept of IAP is tainted for many people and honestly there's no particular reason for it to be in app if it's a case of buying the full game. Also I don't know how you'd even implement it... if someone did an in app unlock of the rest of the game how would you ensure that was DRM-free? If I installed the game on my new computer, how would I unlock it there?


Selling the rest of the game as an unlock DLC (taking the purchase out of the game itself and using GOG's system rather than your own) would be an improvement. That would still avoid making the player download it again, but some might still see it as shadow DRM so it's probably still advisable to sell a standalone complete version.

^This. A demo is great, and with a good cliffhanger it probably becomes a must-buy. I wouldn't worry about the need of re-downloading, most people have good connections and no data caps :P
Alternatively you could do a season's style release like Telltale Games had, where you could buy episodes of a game or the whole bunch. And offer the first episode for free and the rest then as a package.

Sounds like DRM to me... How would GOG provide the complete offline installation files?

That's a great idea! It can solve my problem that, the game would take forever to make if I want to put in all the contents in mind.

Do you mean IAP? I dropped that idea. I will go for SirPrimalform's method of making DLCs or standalone packages.

Definitely go down the demo route.

Think of it this way - and please don't take offence from this - I'd happily buy a game from GoG and trust them with my payment. However, I wouldn't trust a game you wrote to process a payment (even through a known system) and to then provide more content - it's not personal, it's just that it doesn't feel... safe.