For writers that publish independently, it is important to pick the best "Print on Demand" (POD) publisher to fit one's needs. In 2006, after four years of pursuing the traditional publishing route, I decided to pursue the independent/ POD path with my debut novel, Proximity. I chose Xlibris (http://www.xlibris.com/) for a few reasons. First, I obtained one or two books from Xlibris. Physically, they were well constructed, they appeared as good as anything I purchased from a traditional publisher. Second, at the time, Xlibris was a subsidiary of a traditional publisher - Random House. Currently it is part of Author Solutions, which is owned by Penguin Random House. Why is this ownership important? I imagined and my Xlibris sales person confirmed, there was potential for a successful book to be obtained by the traditional publisher - parent company. (Note: I've never actually heard of this happening.) Third, Xlibris at the time touted distribution through Lightning Source (https://www1.lightningsource.com/), an Ingram Company. It turns out, this has huge impact on book availability.
Books reach the market through a book distributor. Bookstores and libraries may have a contractual relationship with only one distributor, or more importantly, may not have a connection with the book distributor that your independent publisher / POD firm uses. Written another way, I've had indie author friends who tried to place their book in a specific brick and mortar store, only to be told, "Your publisher does not really matter to us, it is your distributor...we do not have a relationship with them. Therefore, we cannot carry your book."
Of note, Lightning Source is connected to major retailers like Amazon and Barnes and Noble. Thus, readers can order my indie novel from both stores online, and can even order when in a B&N store through their computer kiosks.
So, when heading down the indie publishing path, ask about the associated distributor and determine where that distributor's books are available.