First of all, the documentation of this module has a lot of problems. The example at the top doesn't work, it has ' in the wrong places, the "native_query" method used for searching isn't documented, and when you do get it to run it just prints out HASH(0x10239485) type of things instead of meaningful results.
Secondly, the module doesn't seem to work properly - the results I got were nonsense, and I couldn't see what I was supposed to do from the documentation. I wanted to search by ISBN but it didn't make it clear how to do that.
In the end it was much easier to write the scraper "by hand" using LWP::Simple and the excellent API documentation of ISBNdb.com than using this module, so my advice is to forget it.