The inspector will place a radon kit in the lowest area of your home (basement) for a period of 48 hours in order to accurately test for radon. During that time, you will need to keeps doors and windows closed until the testing is complete.
Once the test is completed, the inspector will advise the Buyer of the reading. Any reading above 4.0 should be considered for radon mitigation. If this is the case, the Buyer will likely ask you to install a radon mitigation system. Cost for these systems can exceed a $1,000. There can also be a second phase if the first installation phase does not bring the reading down below the 4.0 reading. This is generally rare but in the event of very high readings, it could require a phase two system.
Of importance is that once you have been made aware that radon or mold exists, you must update any Property Disclosure you have that will be given to any future Buyer.
One final comment on radon is that just because your home doesn’t have a basement or an area lower than ground level, you can still have radon. Radon is a gas and can escape through foundation cracks. Even crawl spaces should be tested for radon.