Section 67B. The commissioner may enter into reciprocal agreements with appropriate officials of any other state for the purpose of encouraging vendors in such states to collect and pay over Massachusetts sales and use taxes under chapters sixty-four H and sixty-four I; and, as part of such agreements, the commissioner may waive all or any part of the possible liabilities of such out-of-state vendors for prior periods under said chapters so long as they agree prospectively to collect and pay over Massachusetts sales and use taxes. Any such agreement with such other state is conditional upon such state granting equivalent waivers to vendors located in the commonwealth who do business in such other state.