How to serve correctly - sounds silly?

Surprisingly simple and basic task but there are many players do not serve correctly.

I normally suggest to use their smartphones to record the game (when they are many disputes) and play it back when the opposing side signals a foul serve.

Here's a video showing the correct and vice-versa.

Please note Point-4 and Point-5

or view the view at https://www.youtube.com/watch?v=ladBNB7tGhI

Basically if the shuttlecock flight from a serve is pretty flat and quick, it is usually a foul service.

Some do it for the sake of winning ... where's the satisfaction from such a win?