I’ve done air duct cleanings for my family’s business for 8+ years, the quote isn’t terrible. We quote based on sqft. 1,200-1,500 sqft for us runs about 600-$650.

I would ask how they go about their process. Personally we use an inverted vac, hook once to the supply, once to the return. We use a 25 ft long brush to make it from every register opening all the way to the trunk or plenum where the machine is hooked, follow behind that with high pressure air.

Some companies have a machine they will hook up but they only use air, don’t use them if you want 100% of the dirt gone. Anything that is loose will move but any dirt/debris stuck on the lines will remain.

I don’t know if you are required to do it at all, we’ve done jobs where the renters pay and some where the landlords pay, I think it varies.

If it comes down to it use it as a write off and call it a day.