My experience with deep breath air duct clean

Couple of months ago Groupon had a coupon from "Deep Breath Air Duct Clean", and I did purchase it because I thought it was from Groupon, an IPO company. After purchased, I called this "Deep Breath Air Duct Clean" customer service and mentioned groupon, the woman said the latest appointment slot was 2 months away . I had no choice but waited 2 months.

When the appointment day came, there was no any pre-service call from this merchant, so I called them again and asked if my appointment was still there at 3:30pm. The woman responded that the appointment was 3pm to 5pm, with not kind voice. I was kind of curious how they could complete the clean work if they came over so late. At 5:10pm, two guys did show up, driving a small van, only pulled out one short ladder. What they did was quickly checked the attic and told us they could not do the service and recommended to change the air duct to new plastic. Damn, the total cost was around 3k dollars. Then they left with the ridiculous estimate. I realized this was a scam, starting from purchasing groupon. I did some research that night, and found a lot of useful information from youtube. The conclusion was the usual work of an air duct clean needs about 2 hours using negative pressure vacuum, and my experience was totally a potential scam.

Recently Groupon revised their 1st quarter revenue, and its stock dropped to $14.50 or lower. This trend reminded me to write up above experience with below thoughts:

1. Groupon is not serious about consumer, returning coupon can not return consumer time and spirit
2. Groupon is not careful when selecting merchants
3. Groupon has a lot of discount every day, but these coupons are not the basics of every day life
4. Deep Breath Air Duct Clean is for upsell instead of clean service (from my experience)
5. Air Duct clean is not necessary, the most important part is furnace pre and post filters to ensure air quality. Change or clean your filters instead of clean your air duct. 
6. Under $50 Air Duct clean is impossible, look for some service around 100 dollars if you do need clean your air duct (like after remodel, moving to a new place etc)