As a law professor with a passion for fashion, I’ve spent a lot of time thinking about the counterfeit question. Love ‘em or hate ‘em, here’s the scoop on what’s legal—or not:

Q. Is manufacturing or selling a handbag with a fake Louis Vuitton or Prada label illegal?

A. Yes. You already knew that one. In fact, a provision passed last year allows law enforcement to seize not only counterfeit items but also other things used to facilitate trafficking—like computers or automobiles. So think twice before driving downtown to pick up a load of fakes and then printing invitations to a neighborhood purse party.

Q. Is it still illegal if the buyer knows it’s fake and the seller admits it and disclaims any association with the designer?

A. Yes. There’s still a chance of “consumer confusion” (the test for trademark infringement) among other people who see the bag or upon resale.

Q. What if the bag doesn’t have a logo but otherwise looks just like an Hermes Birkin?

A. That’s a bit more complicated, but for an iconic design, a court might find the bag illegal under a theory of “trade dress” protection. The closer the copy is to a recognizable, famous original, the more likely it is to be illegal.

Q. If selling counterfeits is illegal, why is it so easy to find them online or on the street? In New York, you can even buy unauthorized NYPD T-shirts and hats!

A. Law enforcement is expensive—and there’s an eager market. For some manufacturers, the potential for huge profits makes the risks worthwhile.