Suppliers who are also Customers (or vice versa) may be set up as Two way Traders with the same short code and details.
Creating a Two Way Trader
There is a tick box on suppliers and customers details allowing you to automatically create a two way trader when either setting up a new one or editing an existing trader. For an existing supplier, edit the supplier and tick Create Customer.
Both way traders will be automatically displayed in both customer and supplier ledgers.