A quick scan on ebay shows that you were charging less than the buy-it-now prices.
One other difference is that you were advertising for an event on facebook (as opposed to an external site). Do you pay per click to the facebook page or pay per action (attend or won't attend)?
Great question. On Facebook you pay per click or "per mille" (CPM) - it'd be great if they added "attend" as an event parameter in the Ads API so that advertisers could optimize their ads for event attendance:
One other difference is that you were advertising for an event on facebook (as opposed to an external site). Do you pay per click to the facebook page or pay per action (attend or won't attend)?