Here in the UK eBay tends to be a mix of fully fledged businesses, and "yard sale" type of stuff.
An example of larger businesses selling on eBay is Thomson, (the travel agents), selling some of their holidays on eBay. I notice a lot of small to medium-sized businesses seem to be selling on eBay, too, such as food companies, philately shops, and so on.
I sell Japanese books and artefacts, academic books, and second hand books, and occasional computer bits and pieces.