You can available apis for example this one => https://isbndb.com/apidocs/v2
There are more apis to get books details using ISBN.
Basically, you can have a custom app built for your shop, that app will have a process that will go through all your products with ISBN and get the information about the book using a third api.
PM me if you need help.
Have to say I loved the Sound of ISBNdb but never heard of API before. Do you know how this appears when you add a book. Do I just add the ISBN and it does a search for me just like Ebay does when we sell books or is it different?
I ask as I have shipment of 90,000 second hand books and was looking for easy way for me to upload each book without haven't to copy paste and type a lot of description and other details.
Do you know a programmer that can do the API from ISBNDB?
Sorry lots of questions I'm just can't find a simple way its explained.