In the district of Wan Chai (a fairly touristy area of Hong Kong), there's a fairly well known place known simply as the "Computer Centre". In it, you'll find two floors of a giant warehouse packed floor to ceiling with shops selling everything from a refurbished matte black MacBook from 2006 to an "iPhone 7". I do have to say that the vast majority of the products are legitimate, but there are booths which cater to the less-discerning customers. The great benefit of buying in Hong Kong is that you'll often find products from the mainland side and from the factories in Taiwan.