What does it shows if the books of both supplier and customer show debit balances, how to recomcile?

 Receivable from customers

Advances to supplier

Debit balances of both supplier and customer means we have accounts receivable from them. Reconcile debit balance supplier same as Bank OD  Reconcilation .

Supplier debit balance means give purchase advance to supplier & purchase return .

Debit balances of both supplier and customer means we have accounts receivable from them.