The best way to know if your cleaning was effective is through improved performance of your HVAC system, ideally. You can have before-and-after pictures taken of the ducts (make sure they are of the intake ducts - the ducts that return air into your room), motor and coils. Another tip is smell – sniff the ducts before and after the work is done. Outside of noticeably improved performance, smell and visual evidence are your best indicators.
"Amazing detail and care put into the work of inspecting my soon to be home. I now know exactly hat to expect with no surprises and I have a running head start at repairing all the little things I need. I'm now 100% confident moving forward knowing that New Home Inspections completed this service for me. The experience working with these professionals was AMAZING! HIGHLY RECOMMEND! "