The answer then, is that this is usually a negotiable item. Sellers most often will fix things but circumstances are unique. You'll have to see how willing the seller is to have the work done at his or her expense.
Nothing is written in stone.
By the way, this is a question that your Realtor should easily answer, if you have one and a good example of why you should.
Incidentally, I tell my buyers that I consider it a good thing for the radon to test high - because then a remediation system can be installed and tested and you can have the peace of mind of knowing that you do not have a radon problem. Remember that you can't see it, or smell it, and its level changes - so you may test as within guidelines and down the road have a high reading - if the remediation system is in place and working well, you can rest easy.
Radon is a fact of life in most parts of NJ.
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