College Textbooks
Most college students finish the academic year with a stack of books they won't ever open. What better course of action than to sell them so the incoming class of students can make use of them? Publishers claim that's not cool. In the past, they have sued over it as well.
Textbooks for colleges are notoriously expensive. Even worse, you can frequently find the same books elsewhere for a lot less money. One Thai student made duplicates of the books he needed for Cornell at a significant discount from his friends and family in Thailand, shipped them to him, and sold them on eBay for $100,000. Unbelievable, no? He was then sued for $600,000 by the publisher.
Think about reselling an old Prius for twice what you paid for it, only to be sued by Toyota for the whole purchase price because you took advantage of them. The first sale doctrine, which essentially states that once you buy something, you can do whatever you want with it, is what allowed the student to succeed. even if the maker becomes irate.