A GSA employee shall not engage in solicitation of sales, on or off duty, to any GSA employee under his supervision, at any level. This prohibition applies, but is not limited to, solicitation for the sale of insurance, stock, mutual funds, real estate, computer equipment and any other commodities, goods or services except:

(a) The one-time sale of the employee's personal property or privately owned dwelling; or

(b) Sales made in the course of outside employment of GSA employees in retail stores and under other circumstances not involving solicitation.