There's a trench coat involved
It's important to remember that the red flag-raising trench coat doesn't always come in the form of an actual trench coat.
If you’re hunting for watches on eBay, check out the seller. If the seller’s selling history specializes in expensive Rolexes over cheap electronics and clothes, that's a good sign.
If the Rolex in question is the first watch sold by your guy, raise a suspicious brow. eBay warns that if they claim they got the watch as a “present,” that is a big red flag. Same goes for people who ask for payment via wire transfer or Western Union—but everyone should know that at this point.
Evaluating the seller is a common sense check, and if your gut is telling you no, listen. If you don't want to gamble, save yourself the grief—or the nagging question "is it real?—by using a reputable source like Bob's Watches or Analog Shift.