Yeah, you got scammed. Let me guess, you had to do a bundle link first?

Check your Activity page, see if it lists people you made friends with recently. At least then you can find a link again.

Not much you can do though, you are just out of luck.

Civ 3 is £2.99 and HL2 is £6.99
I think you got a bargain.

Wait. If the gift gets revoked then call Steam Support. If you traded the games in the same trade windows they will probably give you back the gift you gave him.

You said "Did the trade" this means you received HL2?

If yes, Civ3 costs less than HL2 since it was in bundle, what he traded to you a tradable copy? if the trade succeed I would say no reason to worry, but if the guy is suspicious like you say, game may be revoked.

Also, you can ask Humble Bundle support that you activated game in wrong account and they can give you a new gift url.

Bearing in mind I can't even find their site profile anymore.
Check your trade history http://steamcommunity.com/my/inventoryhistory

Also screencap the convo.

Sorry forgot to mention, it was a Humble link for a key. And they didn't send a working code, and it wasn't even the correct game.

You can find their Steamtrade profile by finding their Steam ID, and placing it into this: http://www.steamtrades.com/user/id/############

If you don't have his steam profile anymore, check your recent Steam activity for who you had just become friends with. It may show up there, maybe.

Edit- By Steam ID, I don't mean their profile name, but a 17 digit number that is the same regardless of what they make their personal profile link as. If all you have is a custom profile link, you can get their ID by pasting that custom profile url into Steamrep. That'll tell you what his ID number is.

Heh, HL2 was never bundled and Civ 3 was in a 1$ tier... go figure :)

Am I allowed to post his profile name & shame or whatever, or is that against the rules, I forget?

Atleast report him to Steam Rep, to warn others