You are all thinking from the point of view of the student. And a limited point of view even at that.

Crash courses are great provided you follow two rules:
1. Offer them only during half-terms/holidays (when regular student’s attendances is at a low and you have plenty of free time).
2. Get the payment in advance – and by that I mean this: Crash courses must be booked one month in advance and payment is done at the time of booking. This is very necessary, since you may never see this person again.
What are the advantages for you, the teacher?
1. You will get extra income – I myself charge an arm and a leg for a crash course (since it is much more work for me). A one week crash course – depending on the subject/level – can cost as much as three months regular instruction.
2. You get to occupy yourself (if like me you have no life – except for teaching and piano forum) during the periods when students disappear.
3. You get to really organise yourself and your material, since as Mark Twain once said: “If you want me to give a 2 hour speech I can do it right now. If you want me to improvise something for ten minutes I need one year preparation”. So doing a crash course becomes a huge and invaluable learning experience
for the teacher4. You have the opportunity to evaluate the student – and in case s/he wants to continue with regular lessons later, you will be in a better position to decide if you accept or not.
But there are advantages for the student as well:
1. They will get an opportunity to evaluate you, and they may be so impressed with you and your teaching methods that they decide to become regular students.
2. They will get the exact idea of what is involved in playing the piano. They will then be in a better position to decide if they truly want to invest further in the “piano-playing project” or if they may as well call it a day.
3. They may even learn something!
What would I teach in such a course?
Usually I do either one week courses 2 hours per day five days per week, or two weeks courses 1 hour per day five days per week. The students are always beginners or intermediate (if they are advanced they do not need crash courses, they need master classes).
I cover three areas:
1. Scales and the concept of key – this takes 30 minutes of the lesson and involves learning the theory of scales and chords, how to play them using a modified fingering, and how to do free improvisation on scales. Depending on the student we may cover just one scale, or all the 24 plus modes, chromatic and oher exotic scales (pentatonic, wholetone, blues, etc.) The aim of this module is to convince the student of the fundamental importance of learning scales and how to go about learning and practising them – not how many scales he can play. If he can tackle one single scale and the several procedures to tackle them, he can add the others n his own.
2. Reading and sight-reading music – Another ½ hour. Again, the aim here is not so much to get the student to be a perfect sight reader in a week, but rather to show him how to go about learning sight-reading, so that at the end of the course he knows what is involved and how to go about it on his own (he will also realise that he will need a teacher and lessons on a regular basis).
3. Finally, the final hour is dedicated to pieces. I aim at three pieces (they are all simple), but I will settle for just one. The aim here again is to teach ways to learn pieces, practice tricks and so on. At the end of the week generally the student has mastered at least one piece and now knows exactly what piano learning is all about.
4. If they choose the two week course, then the modules are 15 – 15 – 30 minutes instead of 30 – 30 – 60 minutes.
5. They receive most of the instruction in writing and they are videoed at the start and at the end of the course, so that they can keep studying the material at home.
I hope this helps.
Best wishes,
Bernhard.