Packaging everything together - a decent return
I made this mistake when selling my old film SLR - I bundled together the camera body, two lenses and bag, and got the sort of price I'd been hoping for - when I was thinking of it as a package. But after the sale, I realised that I would probably have expected a higher price had I listed each item separately. After all, I have bought a number of items on Ebay, such as filters, a zoom lens and a flash, but each time I was looking for that particular item.
A few months later a friend gave me his camera with 2 lenses and a bag, along with some extras like a spare film, dust blower etc, to sell on his behalf. He expected around $300 for the lot. I listed each item separately - the bag and zoom lens went in two lots , and the camera with the standard lens it originally came with went in a third lot.
I've now learned my lesson - split items wherever feasible to widen your market. Buying things like cameras in a package makes great sense when buying brand new from a shop as you'll usually save money, but, when selling on Ebay, splitting the items can not only get higher returns, but also makes your item available to a wider audience including the guy who is looking for that particular lens - and then you'll both be happy!