I choose eBay mainly because the Paypal link is available for the buyer to complete the deal quickly. 80%+ of my buyers use this immediately after the auction closes.

Second, ease of use. Everyone's heard of eBay, and I believe it has a wider audience, especially to the new collectors (the ones I run into at the machines call them "collector coins").

"ebay,com" gets me there, "jackpot.com" gets an error.

Third, the layout of Jackpot is somewhat chaotic. Lots of links, all over the place.

Yes, eBay (and Paypal) fees are excessive, in my opinion. Costs of doing business. Commons may not produce a profit, or sell at all. But wait a week or so, relist and the strike will sell (except for Rio Rita, :-)).

I'm sure that Jackpot is a fine site, and on a number of items, the selling price has been higher than eBay's. Figuring a way to do online payments and automatic response emails would help ommensely.