As I always say, no matter what the trade is, buyer beware. Check the company out that you want to hire and ask the right questions, no matter what type of work is being performed. People can be very charming. But once you ask them questions and for proof to back up their statements do they remain nice or do they turn on you like Mr. Hyde? Are they committing fraud?
When it comes to Radon testing with a Radon monitor, the equipment needs to be calibrated on an annual basis. A few weeks beyond the annual date is fine, but no longer than that. A home inspector thought a Radon monitor looked beat up at a home he was inspecting, plus he questioned the placement of the test. He sent me a picture of the monitor. The serial number and manufacture date is shown. When a monitor is calibrated, the lab puts a sticker on the bottom and or side of the monitor to show the last calibration date.
There are a few companies that calibrate Radon monitors in the US. I called all of them, asking if they had record of ever calibrating this monitor. Not one of them did. No stickers on the monitor for calibration, no calibration from the labs that perform that service.
This monitor has been out of calibration for at least 7 years. Every test conducted with this monitor for the last 7 years is invalid. This monitor has been used for testing in Real Estate transactions. Could systems have been installed needlessly? Did this company cost home sellers money when not valid? Its a strong possibility.
If you are selling your home and Radon monitor is being used, check the monitor for calibration stickers. If there are none, ask the testing company where they get their equipment calibrated. Then call that company for proof of calibration. Protect yourself from inaccurate tests and fraud.