Is it possible to link the supplier to customer and vice versa?
A supplier is not always a supplier. He may buy products from us. Similarly the opposite for a customer.
So when making a sales invoice the suppliers too should be listed under the heading suppliers and when making a purchase invoice the customers too should be listed under the heading customers.
In this case the accounts should tally with what he bought to what he sold and the remaining payment to be paid or received should be shown as his account balance.
Creating them as a new supplier or customer will not help with this and later when a customer or supplier statement is issued.