[virginia lurker]

As a home inspector my advise is to make them fix it. If you walk on the contract the sellers and realtor will have to disclose the high level to any other potential buyers and they will remediate or lower the price. It is very rare in our area that radon mitigation is not payed by the seller.
What was the radon level?

[soccermom]

4.8 pCi/L

As I understand it, that isn’t terribly high but beyond the limit.