Here's an interesting story of a self-published Amazon ebook author, James Crawford, who discovered that Amazon "accidentally" gave away his ebook for free
over 6,000 times, and then refused to pay him any royalties. The "mistake" was really a bad algorithm. Apparently when you sign up for Amazon's platform, the company makes you promise to give them the best price, and if they find you offering the same thing cheaper elsewhere, they have the right to automatically lower your price. But, here, Amazon's algorithm mistook a "sample three chapters" that was being given away free on the Nook platform, as if it were the whole book. So it automatically dropped Crawfod's ebook price from $5.99 down to $0. It took weeks to sort out, and by the time that happened, 6,116 people had downloaded the free version.
Amazon then refused to pay any royalties, saying that under its contract, it's absolved from having to pay royalties for such mistakes. While that may be true, I do wonder if there's actually a copyright claim there. Here's another situation where the murky boundary between sales and licenses gets strange. After all, Crawford appears to be technically licensing his work for Amazon to distribute with a specific condition: that it be priced at $5.99 with certain royalties going back to Crawford. Offering it free seems like a clearcut case of an unauthorized distribution, which could be open to a copyright claim.
That said, I agree with the point that many have made to Crawford, that he's probably much better off just using this experience for the publicity, and building on that, rather than suing. Suing would be expensive and uncertain. And, it actually could harm sales, as people often don't like the litigious. Readers might be more willing to support Crawford directly after just hearing his story -- and seeing that he was a good sport about it, who could recognize that perhaps this mistake could lead more readers to his work, and those readers may bring in other (paying) readers in the future. Still, it's yet another case where the difference between physical sales and digital "licensing" becomes abundantly clear.