We do not offer a duct cleaning service. Maintaining a filter on the return side of the heating and cooling equipment is generally all that is needed to keep the ductwork free of dirt buildup. Debris that might fall into a floor register is easily cleaned with a vacuum cleaner hose.
Smudging around wall and ceiling registers is not caused by dirty ductwork, and is rarely caused by a problem furnace. Smudging is caused by the aspiration of air containing particles of dust that are merely being circulated by the forced air system, not being created by it. Improved filtration is the best way to avoid this problem.