There are several ways you could do that. One option is to create two different layouts for starting an invoice. A button on the layouts can switch layouts so you can have a "walk in" button on your regular customer layout and a "regular customer" button on your walk in layout. Both layouts can be based on the same invoice table, but you can devise a number of options for handling the customer data from your walk in customers. The data entered can be used to create a new record in the regular customers table. It can populate normal fields defined in the invoices table or it can populate field in a related "walk in customer" table. They can even be fields in the regular customer table and a script creates the new record in customers and puts the new record's ID into the match field of the current invoice record. Then filling in a customer name, etc. is input directly into the customer table to start a new customer record for your walk in client.