How do you identify an original mobile charger?

A lot of answers indicate you can easily determine this by looking at logos and other markings such as US certification information. These and other characteristics are easily copied and will not be of much help. I have purchased 2 wireless Samsung charging pads from an eBay seller with good reputation and compared them to the one my wife bought at a Verizon store. I could not tell the difference between the three except that the ones I bought both had the same serial number.