Except as otherwise provided in this act, no official of any incorporated town, either elected or appointed, who knows or who by the exercise of reasonable diligence could know, shall be interested to any appreciable degree, either directly or indirectly, in any contract for the sale or furnishing of any supplies or materials for the use of the incorporated town or for any work to be done for such incorporated town involving the expenditure by the incorporated town of more than five hundred dollars in any year; but this limitation shall not apply to cases where such officer or appointee of the incorporated town is an employe of the person, firm or corporation to which the money is to be paid in a capacity with no possible influence on the transaction and in which he cannot be possibly benefited thereby, either financially or otherwise. But in the case of a councilman or president of a town council, if he knows that he is within the exception just mentioned, he shall so inform council and shall refrain from voting on the expenditure or any ordinance relating thereto and shall in no manner participate therein. Any official or appointee who shall knowingly violate the provisions of this section shall be subject to surcharge to the extent of the damage shown to be thereby sustained by the town, to ouster from office, and shall be guilty of a misdemeanor, and, upon conviction thereof, shall be sentenced to pay a fine not exceeding five hundred dollars.