If you want to politely refuse to teach privately in the gym, all you have to do is say that your financial conditions do not allow it. Because private education is expensive, it is necessary to determine whether it is needed according to different people and different situations. If it is not necessary, you can politely refuse and say that you will consider it later. If economic conditions permit, please get a tutor to make progress faster. So you should handle it according to your own situation.