The thing is I wouldn't even recognize an expensive bag, and most of the time I don't even have a purse on me. But I guess the genuine articles are well made, and well my wallet falls apart every few years, so there is that ...
As for the $3 bag, they are being honest, they know it's not real and if it was they wouldn't sell it for $3. They know it's just a bag, any old bag, which for being any old bag is maybe worth about $3.