WHO PAYS for WHAT? "IT DEPENDS. Radon mitigation, and anything else ... it depends". Here's why, ans SUGGESTIONS:
Most "repo" (bank owned) properties are "As-Is, Where-Is"; "REPOssessed" properties from VA, FHA, USDA, local banks, etc.
A NOTABLE exception being the "HOME STEPS" program which endeavors to have the homes particularly "move in ready", and many times with a home warranty; but still beware.
Do NOT ASSUME anything!
Make sure to WRITE IT IN THE CONTRACT "subject to buyer's approval of inspection reports" on all aspects of the property, including but not limited to ... EVERYTHING.
BEWARE of virtually all FORECLOSURE and especially ADDENDA to your "standardized purchase agreement", especially for the "WEASEL WORDS" that makes the addenda SUPERIOR to the contract.
Look out for words like: "Notwithstanding", or "this agreement shall take precedence", and the like, otherwise, you may well be "buying problems" for which the buyer as the new owner, will be stuck with paying.
Buried and leaking tanks, non-hookup to sewer or water systems, past due but not-yet liens on the property for which you may owe, temporary fixes that were done just good enough to get passed the less than diligent inspectors & contractors; and even then, some things just do "wear out" over time, they are of course fine, until then.
WHO GETS TO PAY and is liable for repairs? Unless the BUYER could PROVE, in writing (typically) that the Seller KNEW and actually committed FRAUD (which is difficult to prove.
SO ... know what you are getting into BEFORE you commit to buy.