Last year I purchased a pair of $50 PK2 from a Chinese distributor in Hong Kong to replace a previous pair. Everything appeared exactly the same; the gear, the box, the paperwork. They didn't sound quite right to me though. They were missing what makes the PK2 special. The distributor was willing to take them back but I didn't return them (and pay for the return shipping, hassle etc.) thinking for the price they would make a decent back up pair.
I finally replaced them a few months later with a $79 PK2 from Head Direct. After the break-in period the new PK2 really made me aware of the issues with the previous pair.
I'm not sure if the earbuds from the Chinese distributor were a knock-off or a bad batch, but my 2nd pair (really my third pair) sounded much better.
But to make things even more confusing, my first pair of PK2 was also from a Chinese distributor in Shanghai (but they were $69). They were great. No issues.