Idle fish Some people will publish second-hand teaching materials. Second-hand textbooks are much cheaper than first-hand ones, so you can choose to buy second-hand textbooks if necessary. Idle fish is the App client of Alibaba's idle fish trading platform (iOS and Android versions). As long as members log in with Taobao or Alipay account, they can resell the "bought baby" in their personal Taobao account with one click without complicated shop opening process.