We were at Fan Expo (like Comicon) in Toronto in August (my daughter had a booth in Artist Alley) and eBay had a booth their also (not Artist Alley but the main hall). It seemed it was mostly to promote their app. If you could show them you have the eBay app they allowed you to spin a wheel and you would get a (small) prize. Some of the prizes were Pokemon cards. I myself won a tote bag (can be handy at a show at least).
We go to the show every year and this is the first time eBay was there. There were over 150,000 people over the 4 day event so it gets a whole lot of eyes! Collectors are a big market so it does make sense! I would imagine there would be a number of people that got themselves the app that day if they didn't before.