There's a certain rare, out-of-print book that took me a couple of years to track down. It shares an ISBN with another common, inexpensive, in-print book whose

There's a certain rare, out-of-print book that took me a couple of years to track down. It shares an ISBN with another common, inexpensive, in-print book whose only similarity to the rare one is that it came from the same speciality publisher. Every time I found a copy of the rare book on various used book websites, the common one showed up on my porch instead. Apparently there are a lot of people who treat ISBN as a primary key. A non-trivial number of sellers thought I was trying to pull a return scam on them because they could not be convinced that ISBNs are not unique. The fact that the book I tried to buy generally listed for around $300 and the book I was actually sent went for $15 used really made returns difficult. My search finally ended when a copy showed up on eBay, complete with listing photos. I suspect the price I paid was much higher than usual for a book with similar desirability and rarity because the ISBN collision made it much harder to find.