You can offer your potential customers a free trial of Plesk Sitebuilder Wizard, so they could create a site without any purchasing obligation (see Distributing Link to Plesk Sitebuilder Demo Version).
Users accessing Plesk Sitebuilder in demo mode are called anonymous users, and sites they create are called trial sites. Trial sites have a limited lifetime period and cannot be published until their owners register in Plesk Sitebuilder (and purchase hosting services).
You can at your discretion set up the Wizard for anonymous visits: set a service plan, interface skin, and default interface language common for all anonymous users, configure advertising banner to be placed on every trial site and set up notification messages sent/displayed to anonymous users.