College Marketplace

Is there really a true college marketplace out there? There are a plethora of websites to choose from that sell textbooks and have a huge inventory of books. Still, students can still end up spending over $300 or more on books for one semester and close to $600 for the entire year. This amount of money is still a little high for most students. Would a college marketplace of just students selling to each other solve this problem? I think so because students understand that other students are not loaded with cash so they would price their textbooks reasonably. Instead of looking for new or old textbooks sold by large companies who are only concerned about their bottom line, it would be better to buy from another student who wouldn't mind some extra cash for their book. A student would be less concerned about making a profit then getting rid of their book and making some money on it.