Using the "Can Purchase for Organization" Setting
When an individual to organization relationship type is created, the option Can Purchase for Organization for that relationship is available. This allows non-staff users holding this relationship type to purchase on behalf of their organization.
"Purchase for Organization" in the Checkout Wizard for Non-Staff Users
Enabling this causes users with this relationship type to see the option to purchase on behalf of their organization.
On the checkout screen, users with his relationship type will also have the option to bill to their organization using the Bill this Transaction to drop-down field.
Pay Organization Balances from the My Profile > Overview Tab
On the My Profile page, users with this setting can also see and pay their organization's balances due.