My mother had her furnace maintenance done by someone else few week prior but they didn't have appointments for duct cleaning. She called CanaDuct and they made a quick appointment with an estimate of $250.
Juliano & Fitsum were friendly & professional people who did a good job and even offered to check the furnace, humidifer and everything! The surprise to my mother came when she realized that none of the friendly check up was covered in the estimate and she ended up with a bill for almost $600- very hard if you are retired and just paid someone weeks earlier for furnace maintenance anyway.
After reviewing the other reviews on HomeStars, I reassured her that the work CanaDuct cleaning did was probably good quality work and also reassured her that she was not the only one who ended paying a lot more than the estimated price, that it was likely not a "trick" but a misunderstanding of what the offer to check the furnance really meant.
I suggest that when a worker offers to do something outside of the estimate he tell the homeowner "It will cost about $100 extra, plus parts if I find anything that needs replacing" or something. Otherwise people feel the worker is just being very thorough and friendly by double checking other things (as some companies do) until the bill arrives.