Expensive. Fees are some of the highest (and most complicated) around and can cut into your profits
Less flexibility. eBay policies dictate and require you to take only certain kinds of payments, limit what keywords you can use, put only certain text in your listings and prevent you from cross marketing to other platforms
Restrictions on what you can sell. Inability to sell digital goods (for instance, you are not permitted to sell electronic artwork or eBooks outside of Classified Ads).
Lots of hoops to jump through. There are a large number of complicated programs and policies that sellers have to contort their businesses to fit through or risk limited exposure for their items, higher fees or other penalties. Sellers can waste a lot of time worrying about things like Detailed Seller Ratings when they could be focusing on selling.
Built in prejudices against the platform. You’ll see the exact opposite of this in the next section because prejudices go both ways. Some people hate eBay because they’ve been burned in the past and are now convinced that all sellers are crooks; others have their own personal reasons for disliking the platform. Whatever the reason, listing an item only on eBay can push away some buyers who would otherwise bid or buy were the item listed somewhere else.
It’s harder to sell items that aren’t keyword driven or already of interest. Artists, crafters and authors will especially find that, unless the item they are selling is something well known and often searched for or related to a popular keyword, it will be hard to attract buyers on eBay. It’s a keyword driven marketplace so items have difficulty standing out without a connection buyers might already be searching for.