The report revelead wood-boring or termite infestation.
The buyer asked the seller to remediate the problem.
The seller got an estimate and the wrong estimate was presented to the buyer. The buyer accepted the resolution to the problem in the form of a credit in lieu of getting it treated.
If the both parties had known the actual amount involved, would they still come into an agreement?
The problem here is not who should be responsible but how to settle this AMICABLY outside of closing.