Hobbying isn't one, big market. There are various markets within the industry, and various types of service offerings (think BDSM as a subset within the industry). And, besides volume, there are various factors that define these markets. (Obviously, when having a discussion like this, there are going to be generalities made that don't necessarily apply to all people and all situations.)  

For example, on the low end, in my experience, you tend to find less educated and experienced providers. They also tend to be younger. And, if you're in an incall situation, the location and amenities are often poor. Whether or not the provider is high-volume has as much to do with how well she runs her business as anything else, whether she's working independently, etc.  

The point the author was making in addressing "overpricing" is simply that, like any service, you need to analyze the market to determine whether the service you're offering, at the price you're offering, will garner the maximum demand (or, at least, the volume of business you're expecting). Reading between the lines, in her opinion, some providers with little or no experience enter the market at a rate that isn't supported by their service offering. Their competition will then blow them away, and they could hurt their future earning potential. Her recommendation, based on her own experience, was to enter the middle market, get some experience under your belt, and then decide whether to move into a higher level of service and go after clientele who can afford higher rates.