You guys are just a wellspring of happiness today!
Back to the subject at hand... The customer "feeds" the ATM with cash withdrawn from the bank. The ISO credits the customer's account for the amounts dispensed.
Randy pointed out in a response in this forum a few days ago that the cash dispensing bank could review the ISO's credits to their customer's account as a source of verification. Maytagman, above, mentions getting copies of the statements from the ISO for the same purpose. Either resource, coupled with a review of the amount and cash composition of withdrawals for the same period should provide the dispensing bank with a reasonable, albeit imprecise, reconciliation Trees mentions above. However, it would certainly be easier and more timely if the dispensing bank was able to review its own accounts for receipt of the ACH credits.
Does the ATM owner have any say so about the account the ISO uses to provide reimbursement; i.e. would it be reasonable for the cash dispensing bank to require the reimbursements flow through the customer's business account at that institution or even a separate ATM account as a condition of continuing to do business with the ATM owner?