One important cost of the seller that has not been mentioned in this thread is factoring in the insertion fees of all the times the item does not sell, i.e., receives no bids.

Here is something from an earlier post of mine:

EBay and PayPal are nice to use, especially for high end stuff, but their combined fees come to a lot. If you have a Business PayPal account and use eBay, here are two examples of what the seller pays (for the simplest auctions -- no added features at all):

(1) on a $6.00 opening bid item that has one bid and sells for $6.00, the seller pays $1.14 or 19% of the $6.00 in fees. Ouch!

(2) on a $50.00 opening bid item that has one bid and goes for $50.00, the seller pays $6.15 or 12.3% of the $50.00.