Hubby gave me all of his trading cards and I managed to profit more than 4 Euros in market sales. I might be able to grab a game or two from my wishlist.
Also, for those who are level 8 and above, every 3 votes on the Community's Choice gets you a Summer Adventure trading card. If you don't care about badges you can sell the cards, also if you're lucky you might get a foil card which is even more valuable than regular cards. I got one which was worth 1.45€ alone.
(Even if you're not at level 8, if you achieve that level before the sale ends, you'll get your cards for voting.)