(b) Where the state of New York, any of its agencies, instrumentalities, public corporations (including a public corporation created pursuant to agreement or compact with another state or Canada) or political subdivisions sells services or property of a kind ordinarily sold by private persons it shall be considered a vendor for purposes of the taxes imposed under the authority of sections twelve hundred ten, twelve hundred eleven, twelve hundred twelve and twelve hundred twelve-A and shall be required to collect the taxes imposed by cities, counties and school districts under the authority of such sections.