Radon has no known safe level, and it’s everywhere (A lot like mold)

A Radon Test costs between $150 and $300 in the Madison, WI area. A mitigation system ranges from $650 to rarely above $1,200.

A Radon contingency is one of the contingencies  left out of an Offer when  obtaining acceptance matters more than protection against risk.
Because  Radon gas is everywhere there is air, there will be a level of Radon in every building.  Long term exposure to Radon Gas is a health concern of the World Health Organization; for certain, there is no safe level. The level of 4.0 pCi/L was set by the EPA only as a practical level for indoor air. The chance of a radon level at or greater than 4.0 pCi/L from a 48 hour test is great. (WHO recommends three month tests for accurate indicators). The 48 hour test costs $150-$300.  A mitigation system runs $650-$1200 (If you have a bill for over $1,200 in Madison, WI let me know)  regardless of the size of the house.  A mitigation system will not reduce the level of radon gas to 0. The guarantee made by the people who install  mitigation systems is only that the level will be below 4.0 pCi/L….but again, there is no safe level of radon gas. No one is promising to make your home safe from radon gas.
Including a radon testing contingency will not protect  a person from owning a home with radon gas inside the home. It could be effective in allowing the buyer an opportunity to continue negotiations.  Therefore, the contingency will  be considered for its risk to the seller. If the objective of the Seller is getting safely to closing, and they have options which don’t involve testing for radon gas, the Offer with the testing contingency has less appeal than one that does not.  All things considered, zero risk is more attractive to any owner than any risk. And of course the same goes for buyers. Someone has to give.
Given a choice of contingencies it’s expected a typical buyer prefers to have all the contingencies they can get.  For our part, assisting our clients to become informed typical buyers allows them to decide if any contingency is worth the risk to the appeal of their offer.  A chance to make an informed  choice  to decide what contingencies are best and which ones aren’t worth the risk of rejection, is a level of service informed licensees can offer and others will not.
Radon is everywhere, and  levels can be reduced below the practical level for less than the cost of installing gutters on your house or a bit more than twice the cost of the radon test.   Taking the radon testing contingency out of the Offer is one of the surest ways to improve the chance of acceptance.  Having a radon testing contingency will not ensure the house is radon free.