Well a tough question for sure as there are many who claim to do it.
Just did a sweep out New Lowell way and the install was obviously not done by anybody who was WETT Certified. There are reasons to hire a WETT Certified Chimney Sweep for all your stove need! Why? Well they are the most advanced and highly trained individuals with WETT Certifications.
Yes there are Certified Technicians, but they have only a week of education, the same as a SITE Basic Installer! Yes they should know codes, but that is about it. But at least look for a Certified Technician as the minimum and no less!