In the Chimney Sweep and Stove Repair world there are many things one can not do. In fact it is fairly reasonable to assume that anybody who attempts to do everything is not going to be really good at anything. This goes for those who are chimney sweeps, installers, masons, etc. While the installation of a factory built chimney may be one thing to be a good stove technician and a good mason at the same time is a bit of a stretch. Reminds me of an local company who claims to do roofing and tree work? Really? A tree worker is a credential and certification on its own through the International Society of Aboriculture.. and roofing to be decent is yet another field. So what you end up with is being a hack in both fields.
So yes there need to be other vendors out there who do the work and who chimney sweeps and technicians can use as reference when needed. Common ones of course are stone masons and brick masons, but there are others.