Ask him for close-up pics. Specifically the 90 degree TRS plug. Real Shures have the date code stamped on the plug. If theres no date code on the plug its definitely a fake. Ask him for pics of the carry-case. Real shures have a semi-hard, fabric covered zipper case. It looks like a round dough nut, and is the size of a black hockey puck. If it comes with any other kind of case chances are its a fake.
Does he have a www site or ebay store? Take a look at some of the other items he sells. Does he sell the clear version e2c? If he does, ask for pics of that. The clear version e2c should ONLY have the right side IEM half molded in black. If BOTH R and L sides are half/black, that e2c is a fake... and chances are the other e2cs he sells are fakes.
If he sells other brand fakes (sony MDR-EX, sennheiser MX...etc...), chances are the e2c is a fake.