The use of fictitious USPS Postal Money Orders to scam people out of money is on the rise. In most cases the victim receives the money order and is asked to purchase gift cards for a lesser value. They are told they can keep the difference for their time and effort. There is usually a short due date so that the person is pressured into sending the gift cards before they know the money order is fake.
Anyone receiving a USPS Money Order can verify the status on-line: https://tools.usps.com/money-orders.htm
Or you can call for verification: 1-866-459-7822
The United States Postal Inspection Service has tools to assist with reporting fraud and tips for prevention on their website:https://www.uspis.gov/report
In most cases if someone isn’t okay with you verifying funds, there is probably a reason that doesn’t benefit you. Always be careful and protect your assets!