Many items on Reverb are listed in "B-Stock" condition. These items may have been opened and then returned to the seller, may be a brand new item with a cosmetic flaw, or may have been used as a demo unit in a store. B-Stock items are guaranteed to function as they should, and may even come with a manufacturer's warranty.
It's always a good idea to reach out to the seller of these items directly to determine why they've been listed as B-Stock and what warranty options are available. You can message the seller of the item by clicking the "Message Seller" button on the item listing.