Simplify the following text for a Grade 9 native English-speaking person.
Original: Generally , a book publisher is not required to assign an ISBN , nor for a book to display its number ( except in China ; see below ) , however , most book stores only handle ISBN-bearing merchandise .
Simplified: Generally , a book publisher is not required to assign an ISBN , nor is it necessary for a book to display its number ( except in China ; see below ) . However , most book stores only handle ISBN-bearing merchandise .