Due to it being Giftable Only, it can not be traded (obvious, I know), but due to recent scams (none of which I have seen here), I would require any accepted offer to be sent first, then I would gift Portal 2.
How does that work out when two of you, "send me first and then I gift" guys, try to make a trade? Who sends first?
That depends. I mean, I will walk away from the trade, but some people will try to beg and say they are trustworthy or this or that, and those types usually tend to be the scammers. I have lost games, so if they aren't willing to go first, that is fine, it will just be no deal. But for others, I'm not sure how they deal with it.