I teach brass instruments and all I have is my grade 8 with zero piano skills. I have a friend who has awesome piano skills though and I send my kids to him for exams and things so he enjoys the extra work. Don't have many students, and I charge £12 per hour. My teacher when I was younger charged almost double that, but she had higher qualifications and piano skills. I wouldn't dream of keeping kids on my books past about grade 4 because they need the experience of a piano literate teacher.. but I'm good with beginners, so I'm good for primary schools then they can use whichever teacher their secondary school provides for them.
Don't do it as a proper job, just for a little bit of extra spending money, but I do enjoy seeing the looks on their faces when they pass an exam, or master a new piece that they were struggling with.