Let's say I have Game A for EU only and want a US copy version of the same game.

Is this a trend out there and what is the success rate?

Know any good places for conducting such trades?

Thanks!

Not sure what that means, but asking to private chat for it may be your answer. Not sure we have region locked games here. Perhaps I never noticed.

???
https://www.gog.com/forum/general/regional_locked_games_on_gog_v2
There's, literally, a thread about this topic right next to this in the forum. O_o

If you meant ''EU only; US copy'' -- that was just an example.

As for OP's question - nope, don't know any. Most people just spoof their where-about's to purchase region locked games. As for the legality of it all - yes, technically it's forbidden... but I guarantee you nobody gives a damn if you purchase Postal 2, featuring drugs, in Australia or a game featuring ghosts in Korea, or whatever silly computer game...

I'm surprised there is no place for trading region locked copies.

Someone in US could have an EU only copy and someone in EU might have a US only copy.
By trading, both parties solve the issue and can play with the game they have.

With certain third party legal key sellers that like to apply region lock on game copies, Steam keys experience this issue all the time. I can see this becoming a more common issue for GOG keys too now that bundles feature GOG more often than before. The only thing illegal is that region lock even exists.

Probably because it doesnt affect us?

I admit my ignorance on the matter. It also provides a reason not many talk about it.

Part of the confusion is terminological. Many people use terms like "region[-based] lock" and "region-based block" as synonyms, when -- as far as I'm concerned -- they really should refer to distinct things. The latter is what's actually meant by the title of the thread you linked, and refers to being blocked from buying a given game (or only being able to buy a specialized version of it) due to where you are accessing the store from; the former really should only refer to cases where you're not allowed to redeem a gift code for a particular game (and possibly even to access a game already in your library) because it's locked to the region it was purchased from. GOG has lots of cases of regional purchase blocks (which, in GOG's case, also keeps the store page from being viewed, and the game from showing up elsewhere in the store), but doesn't support region-based locks on codes or owned games, AFAIK -- unlike Steam and probably some of the other major mandatory-client-based stores.

But if someone bought the game and gifted it to you. You should be able to activate it (for GOG)?

Conclusion:
- Region-locked keys don't exist on GOG.
- Certain GOG game pages aren't visible in certain regions. (blocks, as you call them)

Based on everything I've ever heard, yes. (And, once such a game is in your library, you can thereafter access it from anywhere, regardless of geolocation.)