Gamersgate question

That's because of a regional lock, sometimes games for another region outside yours appear as 100% off but don't have the option to buy.

I use GamersGate, and yes, you can buy games as gifts to send them later, or buy something for you that uses a key to redeem it (a Steam Key, for example), but to see the keys, you need to click over a button to reveal them in your profile. Once you click over that you can't send the game as a gift to a friend (but you can send the key anyway :P).

Also, for games that you have to download from GamersGate to play them, if you haven't downloaded a game that you have bought for yourself yet, you can still send it to a friend as a gift. Once you start the download, the option to gift it is disabled, just like the games that use Steam Keys to redeem.

Buying a game for yourself, but not clicking over the button to see the keys or start a download, is the best way to buy something as a gift instead of buying a game as a gift in the first place, because once you do that, the only option for that game is to send it away to a friend and nothing else, and you can't see the keys/download the game in case you "regret" your decision and decided to keep it.