The two I see do their own billing and bookkeeping. They have no payroll except themselves. We have discussed such matters because I also am a sole practitioner who does not have staff and who does my own billing. I have an accountant for my taxes but that is all - and I don't pay her a salary.
They don't all run their businesses the same way. Some have staff and some do not (I would not see one who had any staff), some hire bookkeepers, some do it themselves, and so on. They have business expenses of sorts just like any other business owner -and that can take many different forms. I don't feel bad for them at any rate.