I decline lessons (or end the first lesson early) for the following reasons:
- Some students are looking for a speciality that isn't one of my specialities.
- Some students have unreasonable expectations (such as to be fluent by Monday for a job interview).
- Some lessons have clearly stated conditions but the student ignores the conditions.
I send a brief explanation and ask them to find another teacher.
To minimize these problems, I clearly state that students must contact me before requesting a lesson. Some request a lesson without contacting me. So, I contact them, and if they don't answer, I refuse the request.