C.B.
Buying the fake bags isn't illegal, but selling them is. It's called trafficking in counterfeit goods. Even if the seller tells the buyer they're fake, the minute the seller knowingly sell a knock-off bearing a passable designer label, it's a crime.
If you want to avoid being scammed, purchase legitimate goods from reputable sources. In a small way you will help get the global ecomony get back on track.