More and more I read about self-published authors not bothering to obtain and register an ISBN. The International Standard Book Number (ISBN) is a 13-digit number that uniquely identifies books. Sellers need them to order copies. Book catalogs need them. It is a recognized standard worldwide in the book industry. So why does an independent author not use them? Some say they are too expensive. Others say why bother when they control their own online platform for sales. The long and the short of it is metadata. The industry supply chain is tied to ISBNs. Of course if you have a sophisticated system of collecting your own data or rely solely on Amazon, that is another story. Understanding your market is what it is all about if your are going to make any money from publishing.
In my opinion, ISBNs are inexpensive. You can purchase them from Bowker in blocks of ten. Their database is simple to use. So what could be easier? If you are going to be a legitimate author, for gosh sakes use ISBNs.