Compared to using a duster or changing out air filters, professional duct cleaning means going through all the many elements of the HVAC system. This includes, but is not limited to, the supply and return air ducts, grilles, diffusers, exchangers, heating & cooling coils, drip pans, fans and the air handling unit. Keeping these maintained means avoid problems like pollen, mold or overt dust buildup. This is definitely a problem you want to avoid.
I received a call from the customer service representative that told me that the package I received was for a "Air Duct Cleaning with deodorizing treatment" and it was not a "Air Duct DEEP Cleaning with deodorizing treatment" and that is where the additional $250 was coming from. They then told me that if I wanted, they could come back out a week later and explain it to me professionally and also blamed Groupon for the posting to be misleading. The rep bragged about their ratings on review sites.
If there is stuff in the ducts, the fact that it’s laying there and not being blown into the rooms is proof positive that it is hurting no-one. The 5-6 exceptions you cite in this article I’ll buy, but only with the caveat that at least some of those could have been avoided by proper protection (during remodeling for example) – and if asbestos/lead/whatever winds up in your ducts- the remodeling contractor should be the one paying to remove it.
If I could rate this company a zero I would in a heartbeat. I purchased the service off of Groupon and to say that the groupon was misleading is an understatement. I was at work and my girlfriend was at the house when they got there (keep in mind it took six months for them to be able to get there because they were over booked). They tried to upcharge my girlfriend $250 immediately upon getting there. I told her to put me on the phone and spoke with the guy myself. He said that he would have the manager call me and that he would just start on the service. I received a text from my girlfriend 10 minutes later that the people had left. I never received a call from the manager. They didn't do all vents in the house. All they did was the main floor. It was a pathetic attempt to say the least.
You should be aware that although a substance may look like mold, a positive determination of whether it is mold or not can be made only by an expert and may require laboratory analysis for final confirmation. For about $50, some microbiology laboratories can tell you whether a sample sent to them on a clear strip of sticky household tape is mold or simply a substance that resembles it.