If the Radon Remediation System works, there should not be an issue. Hence, install the system and re-check to show it is fixed before buying. It needs to be fixed. It should be re-check every couple of years.
Is that level in a Basement or in the living area? If it is in the living area, the basement level would be higher. That is fairly high. With Radon, it is most likely that the entire neighborhood/area will have the same problem not just 1-2 houses. Hence, unless you don't want to live in that area, other houses will have the same radon remediation system.
Here's a link to epa
A Citizen's Guide to Radon | Publications | Radon | Indoor Air Quality | Air | US EPA