In reply to your question Peltz, I think it was just someone who really wanted those weapon skins and didn't really know the value of the cards. I can't think of any way he could scam you with that deal.
However as Ganz pointed out, there is currently a holiday auction thing going on; in which players use gems to bid on games. The gems are created by converting some tradables like trade cards and steam backgrounds etc you have lying around in your inventory. This way Valve gets people to recycle the items they don't want or can't sell to anyone.
On the first day of the auction someone bought all three of the items I had on sale for months for 0.03 euro (lowest possible price listing to make a profit on). To convert into gems of course. So if you want to get rid of useless cheap items in your inventory, now is the time to put them on sale.
So in Peltz' case it was obviously a complete coincidence, because he got a lot of things he can craft into gems for some things that can't be crafted into gems.
