The Core Conflict of Interest, in Plain English
Most building owners assume that any licensed contractor can sign off on a compliance inspection. That is partly true. What gets lost in the assumption is that the contractor who installs, maintains, or repairs your equipment has a structural conflict when they also inspect it.
If your boiler service vendor's annual inspection ever flags a problem, two things happen at once. First, they have to either repair it themselves at additional cost to you, or admit they missed it during the prior year of service work they were already paid for. Second, if a violation later issues, the paper trail leads back to their inspection signature. The honest path is to flag everything, even mistakes they may be responsible for. The financial path is to look the other way. Most contractors are honest. The structure of the relationship still nudges in the wrong direction.
The regulators know this. That is why for elevators in NYC, the Department of Buildings explicitly separates approved inspection agencies from elevator maintenance contractors and prohibits the same company from doing both on the same equipment. For boilers, gas piping, sprinklers, and backflow, the regulatory framework is more permissive, but the structural conflict still exists. Whether you address it is on you.
Why this gets worse over time
A building owner who relies on their service vendor for inspections for 5, 10, or 15 years rarely gets fresh eyes on the equipment. Maintenance routines drift. Manufacturer recommendations get out of date. Code changes happen quietly. An independent inspector seeing the equipment for the first time often finds issues that were invisible because nobody was looking for them.