Doesn't sound like you got much which seems to be typical of many of the companies out there. GOOD duct cleaning is expensive but leaves the ducts in great shape The best cleaning usually uses a brush that goes through the duct. Also an multi-headed compressed air wand can do it.

I've never heard of a concrete return in a house but anything's possible. No idea what the sand is for.

You are right to be concerned!

Rotobrush is a great unit for cleaning ducts. Also keep in mind that a contractor will list a price baised upon the average amount of time it would take to clean ductwork in a normal house. A hundred pounds of sand in your return duct is not normal. If the tech was straight up with you and told you it would cost you more because of the additional labor involved, that would be understandable. But making up stories about sand insulation is not acceptable.

Rotobrush is absolute Junk!

Sand and gravel are used as filler around underslab ducting and we often find it inside these ducts near joints that have separated or in the case of metal ducting where it has deteriorated.

Here's how we clean:
Unless the furnace is new, every job begins with the removal, disassembly and thoroughly cleaning of the blower. As applicable, we also access, protect and clean the indoor coil and its drain pan. UV lights are removed, as are sail switches, humidistats and any other component that could be damaged during cleaning. We also clean electronic air cleaner cells, humidifiers, washable filters, etc.
We then connect our vac (truck mounted or portable) to your system with one or more 8", 10", or 12" diameter hoses (depending on the type of vac being used). Each side (supply & return) is isolated and cleaned separately to prevent our vac from drawing additional dirt thru the heat exchanger or indoor coil. Note: The vac used should be capable of moving at least as much air as your system's blower does with a min. of 2500cfm and preferably at least 5000cfm.

We place a live video camera inside the system near where our vac hose is attached. This camera eliminates guessing when each duct is clean by clearly showing the dirt as it is being removed and we welcome homeowners to watch!

An air line is taken thru your home to each of the vent openings. There the vent covers are removed (& hand washed) and our cleaning tools on small flexible rods are inserted into those openings to clean the smaller branch ducts. These tools consisting of whips, sweeps and/or rotary brushes are powered by up to 200psi of air pressure, are used in conjunction with the vacuum to dislodge and remove the dirt. Multiple passes using a variety of tools are made to ensure that all of the dirt is removed! When all of the branch ducts have been cleaned, we access and clean the main ducts and plenum, before switching over and repeating the process for the other side of the system.

Before choosing a duct cleaner, I highly recommend that you contact SEVERAL local HVAC and fire/water/disaster restoration companies to see who the majority refer. These companies should know from experience who does the best work in their area!

A small system with up to 15 vents takes app. 4 hours to clean thoroughly. Larger homes may take all day and those with multiple systems longer. Pricing will depend on where you live and the size of your system.

PLEASE don't be fooled by low advertised (bait) prices. Their hidden fees and fine print often add hundreds of dollars to their bill and many pay commissions to their techs to sell you additional products and services! Your best defense against these types of scams is to insist on a guaranteed final price in writing BEFORE you allow anyone to start working for you and if afterwards you feel that you have been pressured into spending more than you had planned, contact your state attorney general and file a complaint!

I just got my ventilation system cleaned by the duraclean disaster cleanup. I believe the ventilation system is the buildings respiratory system and it should be free from all the infestations. Duraclean disaster cleanup is the best duct cleaning services. People must try it.Get the quality of the air that you breathe improved by duraclean disaster cleanup

Here is a link that might be useful: Duraclean disaster cleanup

Memorable Air Care, we are a NADCA Certified HVAC Restoration " Air Duct Cleaning " Company. Make sure you always hire a NADCA Certified contractor! www.nadca.com

NADCA Certified Duct Cleaner