The shelf costs 50 coins, and can be used to place twelve small items for sale. It requires you to unlock the shelf skill before being able to use it.
Currently, the shelf is the only display that can hold up to twelve items for sale, but it's major downside is that it cannot hold the many diverse items that a Pedestal or Counter can. For example, the shelf cannot hold any shoulder pieces.
Another thing to keep in mind is that a shelf will be under constant interaction, either by you or your customers. As such, you must pay close attention to the durability of your shelves. Otherwise, they may fall apart on you during a business day. The same applies to your counters.
The following items can be placed on a shelf: