Time Will Tell
A good teacher will understand his or her students. They can see who has potential to carry on passing on the skill in the future. They can see the students who work hard, help out, who are respectful and loyal. Of course it can happen that the student might be good and show potential in the beginning, but after a while disappears or even in the end goes against you. So only time will tell if a student really is good, has the potential to carry on the skill. Time is a powerful thing that proves everything. Only the passing of time reveals what everything will be and whether somebody is interested in titles, position or fame – only time will tell.
This means a good student does not need to say they are a good student, time will tell. It is the same with a bad student, time will tell and show them their behaviour and actions were wrong as they will gain the result in the future.
Therefore a good teacher just needs to act normally and behave well and not do too much, never change and spoil their students or offer special teaching. Time will tell, and when a good teacher realises they have a good student they will teach them everything.