2. If the teaching video is purchased through formal channels, there is no infringement if it is resold.
3. If the seller on Taobao is pirated or infringes on other people's intellectual property rights, then as a seller, you should prove that you bought it through legal channels. Obviously, it is difficult to prove that you bought it on Taobao. So there are certain risks.
The infringement of something bought from a treasure is basically certain, but in practice, if the general public does not lift the ban, the official will not pursue it.
Finally, it is everyone's responsibility to protect intellectual property rights.