Why did my book have a different ISBN placed over the actual one?

I have a copy of Pearl Buck's Peony. There was a upc sticker on the back, and when I peeled it off, there was a different ISBN underneath. Why would the retailer do this?|||Many retailers will use their own internal filing system to keep track of books, as opposed to the standard ISBN tag. This helps them identify a book as having come from their warehouse, and also helps cut down on fraud.





If a book has a tag other than the retailer's custom one, it's obviously not from that store.|||It may be that the book has 2 isbns. One is 10 digit and one is 13. The store may have upgraded their system to use the 13 digit ones.





"Enter a 10-digit or 13-digit ISBN in the "Original ISBN" box.


To convert with hyphenation, check the "Hyphenate ISBNs" box.


Click the "Convert ISBN" button to validate and convert the number."