Even with your due diligence, you are still nervous. Not being from a construction or technical background, you have no way of knowing whether the work is being performed as quoted (contractor swapping for low quality materials) or whether the work is even being done correctly (incompetent crew sent to your house).
There is a 3rd party service who provides an industry knowledgeable person to act as your representative. This person reviews the quote, makes sure pricing is inline, and holds the construction crew accountable for their work.
Is this a service that would interest you?
Background: I worked in air conditioning for 7 years, another 8 in industrial construction and commissioning.
I was recently quoted to have my air conditioner’s evaporator coil chemically cleaned and the crew came out to perform the work. The quote included cutting a hole in the ceiling to get access to the coil and then cleaning the coil. The crew that was sent out did not cut a hole in the ceiling and attempted to clean the coil with a vacuum cleaner. After fumbling around in the ceiling for an hour, they packed their tools and asked me to sign the invoice - with still the same pricing as cutting a hole and chemically cleaning. Being familiar with the business, it was clear they were lying to me and I refused to sign the invoice. I spoke with the owner of the company who sent out another crew and the work was done properly. I can’t help but think how many people get scammed by contractors on a daily basis.
Commercial and Industrial construction routinely has owner’s representatives to act and supervise on the owner’s behalf. The issue is partially addressed this with permitted construction. Your town/city/council will review plans and send out an inspector to verify work was done to code. Day to day service work is rarely permitted so things fall through the gaps.
Your public liability insurance would be huge: the risk of being taken to court for wrong outcomes by either party is big. You need to employ people who have the chops: trade certification, and status in their professional body.
A common problem in condos and apartment complexes, is the body corporate lacks understanding of the true cost of services and the building manager charges heinously for a list of certified suppliers, with implicit questions about why they preference some people. We have (for instance) probably bought the wrong kind of floor scrubber, for a $6,000 overcharge. We pay $40,000 p.a. excess cleaning costs for one room which we think is not being cleaned. This kind of thing demands supervision. We had an issue with non-grade screws used to fix glass shelves in units, locks ageing out, which demanded somebody know what was acceptable fixes. Same with AC maintenance cycles, lighting changes, wiring to basement.