From USPS News Link:
Retail employees should watch out for potential money order scams involving “raising” the purchase amounts.
If a customer purchases multiple low-dollar amount money orders, such as 10 money orders for $1 each, the employee should complete the transaction but immediately notify the station manager after the purchase. Employees should never confront a customer about suspected fraud.
Criminals are enlisting people across the country to purchase low-dollar money orders and ship them to New York, where the amount on the order is changed.
When accepting a postal money order at the window, make sure the plural “dollars” appears if the value is greater than $1. There should also be no discoloration around the dollar amount, which could indicate it was changed.
If the information does not match postal records, the money order has likely been altered. Retain the postal money order and call a local Postal Inspector.
To ensure a money order is legitimate, call the Postal Money Order Verification System, 866-459-7822, 48 hours after the issue date and enter the 11-digit serial number, dollar amount and 6-digit Post Office ID.