If you've sold something online and the buyer sends you more money than the item sold for, make sure to ask more questions. If that person asks you to wire or transfer funds to them for the overage they sent via Western Union for something bought from you, make sure you verify the transaction with the credit union before processing.
If you've received a deposit in your account that you are not familiar with, make sure you verify that doesn't with the credit union before using those funds.