Sort of had this scenario happen to me.  Plot plans are required in Mass & ours disclosed a zoning violation & fence encroachment prior to our purchase.  I wound up having to search for records  filed in City Hall, but not in the ROD & then deal with the zoning violation  before we could go through with the purchase.  I think that at the time the plot plan cost around $125 & turned out to be worth every penny we paid for it.