Depends what you are buying. Some products are far more commonly copied than others, and with varying degrees of inferiority to the original.
I knew it was bad beyond recovery when I started getting counterfeit books.
I came across this issue when I was pondering whether to buy the English edition or the Japanese edition of Uncle Bob's Clean Code. Luckily I saw the reviews saying that the English one was counterfeit, so I went with the Japanese one instead.