I've seen a trend lately of "teacher shopping." People don't commit to a set of lessons. They want to see how one lesson goes with a particular teacher. In some cases, one lesson is all you need to see how the relationship and learning will develop. In other cases, it will take several lessons for the teacher to develop a sense of how the student should progress and what aspects of their playing need to be worked on the most. In this situation, one lesson will not be sufficient.
This brings me to my next topic: loyalty to a certain teacher. How do you know when you've found the right teacher? Well, sometimes you won't know immediately. In our society, we often move on to the "next greatest thing" so quickly without letting things mature, grow, and flourish. I'm here to say that the relationship between piano teacher and student is so precious that it can not be replaced as quickly as we change phone devices and hair colours.
The bond that is created between teacher and music student can be incredibly strong. The student reveals so much of their inner soul and character through the study of music. The trust that is developed can be very deep indeed.
So, what does all of this mean about knowing when you've found the right teacher? It means that you'll hear your playing getting better because you trust that the teacher is knowledgeable enough to help you and you don't need to go to someone else. You'll know you have the right teacher when you can tell that they bend over backwards to make you feel comfortable - but at the same time, challenge you.
My advice is this: once you find that person - stick with them and don't leave. Stay with them and attend lessons weekly at a committed time. Show your loyalty to them as a sign of respect. Does that mean you shouldn't attend masterclasses? Of course not! You definitely should. These are fantastic learning opportunities. Nearer to a performance or exam it might be wise to play through your repertoire for a second teacher just for the experience. Please note, this experience should NOT be to change everything you've worked hard to accomplish with your main teacher.
While there are often very legitimate reasons to leave a teacher's studio, more often than not, we should simply be loyal and steadfast. Music teachers are highly-trained and highly-committed individuals who help bring beauty into the world by sharing their knowledge of our beloved art. So, next time you want to "test drive" a new music teacher, think twice. The teacher-student relationship is not one that can be discarded as easily as a piece of technology.