There are many ways to handle suspected fraud. One completely reasonable approach would be to talk to customers about scams if fraud is suspected. You can still

There are many ways to handle suspected fraud. One completely reasonable approach would be to talk to customers about scams if fraud is suspected. You can still leave it up to the customer to decide to go through with the transaction. Other approaches exist too. But doing absolutely nothing and quietly proceeding with the transaction is just hostile to your most vulnerable customers.