Home sales move quickly, so EPA has separate radon guidance for buyers and sellers: test the lowest level a buyer could use, guard against tampering with the test, and fix the home if the average result is 4 pCi/L or more (EPA, Home Buyer’s and Seller’s Guide to Radon).
The guides below cover radon inspections and what each side of a sale should ask for. If a test comes back high, see radon mitigation and what it costs.