We've had a REAAAAAALLLLLLY big scammer issue here.
Few people are very trusting thanks to this, and there's been scams before similar to what you're proposing. If you really do have a Witcher 3 GOG key, you'd better have some darn good proof. I'm also interested in hearing how you got it.

ok best of luck.
[I agree with the man above.

....you just now made an account to point this out? O_o

it is 23 usd/euro on cdkeys, probably the keys will be revoked

Have

Wolf Among Us
Back to the Future Telltale
Still Life Bundle Still Life 1, Still Life 2, Post Mortem
Return to Mysterious Island 1 & 2 Bundle
Poker Telltale
Poker 2 Telltale

Want

Wishlist.

And any Adevnture, Point & Click, RPG and Civ type games I don't have

Note to Scammer - not trading first with anyone without trading history so don't waste both of our time

oops something went wrong

Want:
Painkiller Overdose (GOG)

Have:
Knights and Merchants (GOG)
Wasteland 1: The Original Classic (GOG)
Age of Wonders (GOG)
Defender's Quest (GOG)
Star Wars: Dark Forces (GOG)
Divine Divinity (GOG)
Edna & Harvey: Harvey's New Eyes (GOG)
Men of War (GOG)
Duke Nukem 1+2 (GOG)
Duke Nukem: Manhattan Project (GOG)
Duke Nukem 3D Atomic Edition (GOG)
A Bird Story (GOG)
Consortium: The Master Edition (GOG)
The Secret of Monkey Island (GOG)
Monkey Island 2: LeChuck's Revenge (GOG)
The Dig (GOG)
Outlaws (GOG)
King of Dragon Pass (GOG)
Arcanum (GOG)
Vampire: The Masquerade - Redemption (GOG)

...

I got a trade offer for you.Check PM :).Cheers

Thank you for the trade! :)

You're welcome.Trade was beyond awesome :D.Hope for more of these in the near future ;).Cheers

Nevermind

Have (all Steam keys):

)
1993 Space Machine
100% Orange Juice
A Fistful of Gun
Another World – 20th Anniversary Edition
Crawl
Divekick
Door Kickers
Duke Nukem Forever
Elegy for a Dead World
Flying Tigers: Shadows Over China
Gods Will Be Watching
GRAV
Inquisitor Deluxe Edition
Infinifactory
Lethal League
NOT A HERO
Noct (Early Access)
Oceanhorn: Monster of the Uncharted Seas
OlliOlli2: Welcome to Olliwood
Puzzle Agent
Puzzle Agent 2
Prison Architect
Punch Club
Reus
Road to Ballhalla
RONIN
RollerCoaster Tycoon 2: Triple Thrill Pack
Runestone Keeper
Shadowrun Chronicles - Boston Lockdown
Sam & Max: Devil's Playhouse
Silence of the Sleep
SolForge — Dinosaur Starter
Strong Bad's Cool Game for Attractive People: Season 1
Stronghold Crusader 2
Super 3-D Noah's Ark
Steredenn
The First Templar - Steam Special Edition
The Darkness II
TransOcean: The Shipping Company
Tropico 5
Ultimate General: Gettysburg
Universe Sandbox
Viscera Cleanup Detail - House of Horror DLC
Wasted
WARMACHINE Tactics
WARMACHINE Tactics - Mercenaries Faction Bundle
Club Manager 2015
Fly and Destroy
Legendary
Insecticide
Gravi
Bunker: The Underground Game
Point Perfect

Interested in Mushihimesama from the current Steam sale: http://store.steampowered.com/app/377860/

I bought the key from g2a

In that case, I hate to tell you this, but you're screwed.
Nobody around here trusts G2A. Keys from there usually don't work here, and a lot of fake GOG keys are sold there. The chance you're going to get somebody to trade for it is next to nil.
I'd advise you look into trying to get a refund if you possibly can. If not, I'm afraid you're going to have to just accept it as a loss and move on.