Anchorage Police detective Clinton Thomas knows money. He has seen all kinds of counterfeit bills as a member of APD's financial crimes unit.

Thomas shared tips on how to avoid being ripped off after a man was scammed after advertising a watch on Craigslist. The man was asking $4000 for the watch; a man paid him that amount in cash-- but all the bills were counterfeit.

Thomas offers several tips to avoid being bilked with fake money, especially when a lot of cash is involved. He says conduct the transaction in a bank.

"You want to make sure your currency is good. What better way than to have a professional bank teller, or person look at that, and verify that right on the spot for you," Thomas said.

Thomas says most $10 and $20 bills have a watermark of the person on the bill. When you hold a bill up to a light you will spot a secondary face on the right side of the money. There is also what's called a security thread that runs through the bill. It will read, for example, "USA Twenty" for a $20 bill.

There is also color-shifting ink that indicates a bill is real. On a $10 bill, you will find the number 10 on the right bottom corner. When you hold the bill at different angles, the 10 will change colors.

Not all bills have the same security features. You can see those features for yourself at uscurrency.gov.

Editor's note: An earlier version of this story gave an incorrect web link for the uscurrency.gov website.

Copyright 2017 KTVA. All rights reserved.

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