I've seen price matching online, but it usually refers to non-sale prices, and you always had to show a real site selling the game. It's no different than price matching in brick and mortar store, which also want proof.

Regarding the original topic, asking people to mark what they have can work to an extent, and would be a nice site feature (mark which games you have elsewhere or in physical form), but in practice it's probably not a great boon to GOG. Still, all the sales elsewhere reduce the chance of me buying something at GOG (or at Steam for this matter), and a higher discount of individual games might have gotten me to buy something.

Only on some bundles. For most of the bundles they don't even do that and the duplicate game simply disappears (unless they've changed their policy in the last few months and I didn't notice yet).

But anyhow, I completely agree with you that the GOG bundles are much better. It's great that the bundle page knows which games I already own on GOG and discounts those games from the price of the bundle. I'm not going to buy every bundle because I'm not interested in every type of game, but for the bundles that do catch my eye I have no problems paying the bundle price even if it means I get a duplicate of a game I own on another service.

If I really like a game, then I probably want the GOG version at some point anyway. It's digital which is an advantage if I already owned the game on disc since I don't have to keep finding my discs anymore. The lack of DRM makes it easier to apply fan-made patches and mods especially compared to the Steam version. And some games are patched to run better on newer versions of Windows plus have a lot of digital extras, which is more than I'd get with either disc or Steam.

So even if I already have the game in another format, the GOG version is usually better and I don't regret re-buying good games on GOG. It would be different if I didn't really like the game that much to begin with since I don't intend to replay it, but the few times that's happened so far I wasn't really interested in the overall bundle anyway.

And on a side note, I think the GOG interface has improved since the last major sale and I find it so much more convenient than Steam's now. I love how it marks off which games I already own when I'm looking down the list. Steam doesn't do that, and it's kind of a pain switching back and forth between my library and the store page to see if I already own certain games on Steam. Steam should do the same thing as GOG where it indicates if you already own a game right on the list of specials.

There is a browser plugin for Firefox/Chrome which adds this functionality and much more: http://www.enhancedsteam.com/
http://www.cheapassgamer.com/topic/301685-official-enhanced-steam-discussion-thread/

Daaaww. Poor you. Here, have a +1. (The first one is free. If you need more, you know where to find me. ;-) )

What are you talking about? With Steam you just buy the games individually for 75% off each.

Buying a bundle just decreases it even further.

Whether the original is 50% or 75% is not the point. For example, the tomb raider bundle is now 69.99, but buying each game separately, it would cost 116,90. That's 40% off by default (during a sale, that might do down to a 75% both, the bundle and the games each). The point is that if I already own, let say, the last Tomb Raider right there in Steam, I can't buy the bundle without that game, paying only for the rest of the games, and still getting 40% off.

That Steam sales are typically 75% off, instead of 50% as in GOG (for individual games at least) is a fact, but is the price to pay I guess for having DRM Free games.