There are lots of things that can come into play during the sale of home. What has more recently been at the forefront is the "due diligence period" that is allowed once a contract has been placed on a given house. This gives the buyer an opportunity to look closely at the house to see if it qualifies as one that is a viable choice. Most of the time buyers contract "home insepctions" to be performed that can help identify potential issues that may be prudent to address BEFORE the sale. With increasing frequency, educated buyers are requesting that "certified radon test professionals" conduct radon testing to determine if radon exists in levels in the home that the EPA has determined to be a "potential" health concern.
You should never NOT buy a home because it tested high for radon. If you like the house, it can always be FIXED "safely", "cost effectively" and with minimal cosmetic intrusion by certified mitigation professionals.