Imagine complaining about a "business" where your customers never receive an invoice, have unlimited access to your product,  thus don't care how much they use or how much they are billed.    Imagine that these customers are in a practically limitless supply - there are more customers than your practice can handle.     If you want to see more customers, simply work longer hours, or crank them through faster.

Compound this with no collections risk, no need to advertise, and never having to worry about being laid off in a downturn.

THAT is a medical practice.