So you can write about computer network and veterinary services all the same?
Yes. I routinely write high-quality essays for very satisfied customers on topics such as Criminal Justice, Business, Law, Nursing, Psychology, History, Philosophy, IT Security, Veterinary Science, Sociology, and Education. That's not a complete list of my range of subject-matter competency and there are certainly some subjects that I don't handle at all, as well as specific topics in some areas that I do cover more generally. The url link next to my name icon goes right to a more complete list of most of the topics that I handle (routinely).
It would be impossible to make a living at this if you can't write intelligently about a wide range of topics. The fact that you obviously think it's so remarkable that anybody writes in more than a single subject area might help explain your apparent resentment and vindictiveness toward those of us who actually do this successfully for a living. We don't need to "compete" by trashing other writers and making false statements and implications about them.
I'd humbly suggest that customers consider the way writers treat other writers on these public forums provides a glimpse into their character and that you should stay clear of those who resort to tactics like attacking other writers, especially under the cloak of anonymity. Those of us who are legitimate (like ProfessorVerb, ResearchPro, JohnsMom, AndyWoods, 99Essays, and me) maintain respectful relationships with all of our legitimate competitors and we always identify ourselves in our posts.
Full Disclosure: PV, RP, JM, and I all do write for some of the same commercial essay companies. We all compete against one another on the company sites and for freelance work. None of us owns or is otherwise employed by any of those companies and we have no other relationship or mutual interests at all.