Fan blades and blower fins do not always get cleaned when mechanical services are done. Dust build up can cost your $$!
Residential vacuums are not designed to reach deep into the duct system.
We have HEPA filtered vacs and equipment designed to completely clean the ducts.
Filters should be change often.
A visual check and periodic cleaning will give you a good indication of the debris level in your ducts.
Cleaning the duct work in your home will improve the indoor air quality.