If one of your customers is also a vendor (or vice versa), add the person's name to both your customer and vendor lists, but vary the name slightly or tag the name with an identifying letter or number.
For example, if you have a customer named Brenda Bowden, you might list her as:
Brenda Bowden_C in your customer list
Brenda Bowden_V in your vendor list
To make sure that the person's actual name prints on invoices and checks, enter the person's actual name in the "Bill to" field for customers and in the "Print on Check as" field for vendors. These fields are at the bottom of the Address Info tab in the New Customer and New Vendor windows.
Choose Customers > Customer Center.
At the top of the Customer Center, click New Customer & Job and then click New Customer.
Choose Vendors > Vendor Center.
Click New Vendor.
Note: QuickBooks can't:
Convert a customer to a vendor (or vice versa)
Merge customer and vendor information