DreadTalmage posted something very helpful (page 2) in response to this Forum question by dgordon. Here's what DreadTalmage has to say about money orders:
You may already know this, but I believe it is important information none the less. After years of working in a bank, it seems money orders are the highest risk. When you receive them, check for a 1800 number printed on either the front or back of the MO. You can call that number and verify the MO has no stop payments and is an authentic MO. Also, find out how long your bank will hold the funds to make sure it is not counterfeit. The institution I worked at held them for 10 days, no exceptions. It seemed the postal money orders were most likely to be counterfeit, whenever I have been paid in those I usually take them to the PO to cash as that way I can know right away if they aren't legit.