a mitigation system will turn this "bad" thing into sth good, since u have better flow and control of the radon. A easy sel f-test set can be bought and u can do regular test every year at $20. for the normal house, maybe someday the radon will come out and need this sy stem. btw: if the seller didn't disclose this info, he should get this fixed before closing. you agent should help u to communicate. if not fixed, the lender might ask some trouble during closing.
True, Radon problem in New England is like termites in Texas, if you find it , you fix it. But nobody cries wolf about it. Simply because a common problem is not taken seriously.