If you have a business, or are able to as a hobbyist write off extra expenses, good for you.
I am incline to be more in Cliff's camp;
For somone considering selling off stuff on the side, you are better off selling locally through craiglist or kijiji - the fees I had, between listing, final sale, and paypal FAR exceeded this 15%(+/-) figure;
if they are high value items, I could see it being worth your time, but if you have money into said parts, odds are any profits you might think you have netted at time of sale, will be relegated to virtual pennies after the fact.
ebay made several changes that did nothing but penalize sellers - especially small timers like myself.
(i used to have sellers feedback, if it's more than 12 months old, I believe it's essentially deleted)
I still look for items there;
I have bough on average a half dozen items a year there for the last several years - but used to buy A LOT more.