World religions, as a course in college, is an intense study into the numerous ways that different cultures view the afterlife and God or gods. It may also include non-religious views (e.g. atheism). If your professor is teaching the course as a comparative study, you may find that you will have to write a paper comparing more than one religion to others. That requires a lot of research and numerous texts, some of which may be out of print. A used bookstore can help you in your paper-writing endeavors for this class in all of the following ways.
Locating out-of-Print Texts
Used bookstores are very good at locating out-of-print books for you. They may have a few of the texts on hand already, and the rest they can find by perusing used book data bases that would take you days to search for and search through on your own. These older copies of the religious texts that you want to use for your paper will require some time to find and acquire for you, but if you are proactive and request them from the bookstore far in advance to your paper's due date the store should be able to get the books for you.
Examining Antiquated or Fragile Texts
Some used bookstores do acquire antiquated and valuable versions of certain religious texts. While you may not be able to afford these texts outright, you may be able to visit the store in person and request a few minutes to examine certain passages in these texts for their comparison value and source information. For example, a grimoire from the days of Salem witch trials or a Quran that has numerous gilded drawings in the margins may be in a used bookseller's possession, but you could only handle the text with white gloves and in the presence of the bookseller. Still, it would be an invaluable source for a comparative study on religious texts and religions.
Providing Information on the Known Number of Variations of Any One Religious Text
Finally, a used bookstore is a good starting point for learning about the numerous variations of any one religious text. For example, the Bible has seen several translations throughout its history, and more recently a dozen variations of the "updated" version of the Bible have been produced. If this is something you would like to explore as a topic for your class and your paper, the used book store can show you how many different variations there are, what they are titled or subtitled, where to find them and how to find them. Likewise, many other religious texts would have similar information that you could acquire from the used bookseller.