When sending an international wire transfer, the transmitting and receiving financial institutions both (usually) assess fees associated with the transfer. These fees can be accurately anticipated by clearly asking the banks, providing examples of dates and amounts, etc. Prior to executing a transfer, the sender is asked to approve the transaction with clear disclosure of the fees that the sender must pay to have the amount conveyed to the beneficiary.
However, the amount that the beneficiary actually gets is notably less (in examples I've heard about, about USD$65 to USD$130 less) than what should have been received after accounting for previously disclosed fees charged at both ends. Presented with the sender's receipt showing the full amount reaching the recipient, the recipient financial institution blames an unspecified intermediary or correspondent bank for taking the missing money. These intermediary fees are sometimes hefty enough that the transaction would not have been ordered if the sender had been fully informed about the costs, and in the relevant cases the sender made every effort to fully learn about the costs in order to make an informed decision about the transaction.
This violates the model of paying a supposedly-trusted pair of financial institutions a clearly discussed and disclosed fee for conveying value between parties (which, if the bank is making a profit on the fee, should also cover the costs of any service providers these financial institutions choose to work with to deliver the service; banks may choose to lower or waive fees as a convenience to customers so as to incentivize customers to generally keep deposits with them where the bank can earn interest on lending those deposits). If they cannot be trusted to deliver the full amount, but instead keep an unpredictable portion along the way, the customers might prefer to choose alternative means of transacting.
What can a sender do to find out about these extra fees, in advance of having to pay them?
For this question, it's OK to assume the sender has an honest and completely cooperative beneficiary.