Why can't hearing AIDS be bought online?

Hello, hearing AIDS belong to the second class of medical devices. According to national regulations, it is necessary to control their safety and effectiveness. Therefore, hearing AIDS can't be sold online. It is generally recommended to go to a professional fitting center for fitting. In fact, the reason is very simple. If there is no formal fitting, it is easy to buy hearing AIDS that are not suitable for your own situation. The hearing aid bought online has not been debugged, the amplification is excessive, and the sound is very noisy and harsh; There is no amplification, but I still can't hear clearly with a hearing aid. Originally, it was a good thing. If you don't do it well, you will lose more than you gain.