On half.com (affiliated with ebay) there is a thing that is called an ISBN number. I am trying to buy?

my textbooks from there, so what I did was called my college bookstore, and asked them for the ISBN, edition number, and year of book. They gave me all the information,and I am searching for it on half.com, but the ISBN number on half.com, is not the same as the one they gave me at the school, but it is very similar to it though (it's like the first few numbers in the ISBN are the same as half.com, but the end is not). So, my question is should I trust this buy, although the ISBN number is not the exact number decribed by the school, but on half.com they do have the edition number and year number correct? Should I go ahead and make the purchase because it is cheaper buying books on there than buying it at the school bookstore.|||No. An ISBN number is as unique to a book title/edition as your DNA or fingerprint is to you. If your school says the ISBN number you need is not the same as the one your buying, you may not have the right edition of the book. Make sure to look at amazon.com or do a search for used textbooks, there are many sites to buy from.