B&N will sell any book THROUGH their store. If someone knows it exists, they walk up to the counter and request a copy in person and pay on the spot.
Locally, a single B&N manager can opt to shelve local author titles in their one store on consignment (you buy them, B&N resells them for you).
Regionally, it's B&N's (public) policy not to carry POD books or host the authors of such books for signings. The books aren't always there on time, they're not returnable for the same consideration as commercial books, and the quality isn't up to standards. If they get a bad book (loose pages, curling covers, fading ink), they'd have to jump through hoops to get them returned, never mind what they'd run into if the book just didn't sell and was clogging the shelf space. The books also can't compete in the market because of the prices, so it's good business for chain stores to NOT stock them on shelves.