I would never know how to approach a girl with a trade. It is a pain in the butt to try to trade/sell on craigslist so I can't imagine how a guy would be able to bring it up to a girl. Maybe I should start sending out pm's asking if girls here would want a year old Mac mini for some fun
I guess some stuff could come up in chit chat, bit then I would be hard pressed to make the offer. Even for services from me, but that might also be because in the field that I work in there is a gap between what girls would want and my expertise. Most would only find what I did ten years ago useful but that is the stuff that I am rusty with and have advanced much past it career wise.