Fair enough, but isn't that like saying every car salesman needs to do the "hard sell" to get anyone to buy a car. In my experience, that isn't necessary all the time, and most times it isn't successful.
The issue isn't about whether the hard sell is always necessary, its about being smart enough to do whatever you need to in order to get someone to book with you again. What I wrote was a general rule of thumb to help conjure the correct mentality to have success.
For example...
If someone tells you that they want to book at a later time and gives an excuse that he doesn't know his schedule for next week, whether it is the truth or not, he will just hold a fixed position on this and you will get nowhere.
Better to do this...
Firstly you need to get his number through normal dialogue:
Teacher: Okay that's fine, just let me give you my number so you can phone me when you know your schedule
Pupil: Oh Okay Sure...
Teacher: Would you just give me a one ringer just to check you got the right number and if you call me and I have your number, it also lets me know that it's a call I need to answer.
Pupil: Hmmm, okay....
Let's assume the person is lying. The pupil is trapped into that lie and now it's your leverage is to get them to book again. Up until now they are happy because they think that you are leaving it up to them and that they can just not call you instead of having to confront you which they definitely fear otherwise they wouldn't of lied in the first place.
Now you need to close the deal just before the pupil leaves.
Teacher: So when do you get your schedule?
Pupil: Maybe around Saturday or Sunday.
Teacher: Would you like me to phone you?
Pupil: No it's okay, I'll phone you.
Teacher: Okay, no problem, so I'll probably hear from you around about the weekend.
Pupil: Yeah, I'll maybe phone about then.
Teacher: Okay I'll tell you what, if I don't hear from you by lets say Tuesday I'll give you a call just to see what's happening.
Pupil: You don't need to do that, I'll phone you. Don't worry it's fine.
Teacher: Yeah I know that it doesn't really matter because you'll be phoning anyway but I'll just say that just in case so I that I know what's happening.
Pupil: Okay lets just see, anyway I have to go...
Now don't phone with the mobile phone you stored his number on because it will show him it's you, so phone from another line. Ask him "Did you get your schedule?" and "When would you like your lesson".... Now he's forced to confront you or book and he thinks it's all of his own doing - the pressure is strong. Eventually you will get into a routine and the guy will keep coming back regardless of your teaching ability.