OK, I post something on ebay. They charge my Visa card $0.30 (or whatever) for doing that. It doesn’t sell, so they don’t get a cut of the final auction fee. So it’s just $0.30.
Now it’s my understanding that a retailer (ebay in this case) has to pay Visa a % of all transactions. So what does ebay pay Visa, $0.01? Since there must be millions of users in similar situations, does Visa like getting paid in a million $0.01 transactions each month? Or is there some clever way they all get lumped together?
Ebay has to pay Visa a percentage of the revenue that is charged through Visa cards.
In your example you were charged .30 by ebay for an auction that didn't sell. This means you owe ebay .30. Let’s further assume (following your example) that ebay’s agreement with Visa has a negotiated 3.33% commission (in reality it’s probably much less due to ebay’s size, but smaller merchants may pay something along those lines). So you get a .30 hit on your Visa card, of which ebay gets back .29. So the actual transaction is not .01, it's .30. And since it’s all done by computer, it’s not a big deal for Visa.
Now, I actually find it unlikely that there are millions of people running one auction a month with no sales. I’m sure there are some, but I’d guess that the majority of ebay sellers have mostly successful auctions (otherwise they’d probably stop after the first couple of items didn’t sell).