You can purchase an item for a guest on behalf of a customer.
Click the Blue Cart Button
Find the client that will be paying for the item
Search for the item you want to charge
In the cart, click the grey dropdown box to purchase the item for a guest
Choose "Guest"
Search for the client or add a new one
Click purchase
On the profile of the client that paid for the item, it will show who they bought it for
On the profile of the guest, it will show what the item is and who purchased it