The soliciting, selling, exposing for sale, or offering to sell of any goods, services, articles, wares or merchandise of any nature whatsoever, within the boundaries of Central Washington University property is prohibited except by written permission of the board of trustees, president, or his designee: Provided, That this section shall not apply to any otherwise legal private, personal, noncommercial sales between individuals where no general or public solicitation, exposure for sale or offer to sell is involved, or to the soliciting, selling, exposing for sale, or offering to sell of individual books, newspapers, magazines, pamphlets, and similar published materials.