Dear Rangarajan,
Auditor can identify such transactions in the general ledger where payment is made to vendor with no corresponding entry for debiting expense due to non-availability of bills.
During vouching, may be the internal journal entry or purchase voucher alone would be there without the supporting bills.
Solution to the problem:-
1. Materiality of the transaction to be noted.
2. If amount involved is greater, Auditor can insist for duplicate bills.
3. If the Vendor is regular and if many transactions for more or less same amount is done, auditor can confirm the validity of the transaction by the payment made to Vendor. (With corresponding verification in Bank A/c Statement or Properly authorized Cash Voucher )
(Provided the vendor has stopped supplying thereafter) (If he is regular and continuing, then we can insist for duplicate bills or statement from vendor)
4. Management can give a representation if the amount involved is significant in the balance sheet & profit / loss Account point of view and no duplicate bills could not be availed.
Hope this helps u
Regards,
gurusanthanam