The official line:
Hong Kong does not allow fakes, or misconduct of business ie changing false parts as someone above who obviously dont know HK, mistakenly say so. The law enforcement is absolutely strict on this, especially in a busy touristy place as TST or Nathan Road, it's just stupid for any crooks to go against the law unless he's dying to get into jail.
The cheap cameras could be of unknown or cheap brands. It could also be not 100% made in Japan, as most international law depicts that only a certain % is made in that country, the product could then be claimed as from the country. The camera could also be "water product" ie with no guarantee or after sales service. If you're not comfortable with it, you could make the purchase in reputable stores like Broadway or Fortress. Hong Kong Consumer Council is one of the best such organization in the world in the protection of consumers rights. In case of any doubts please log onto the Consumer Council website.
Almost ALL of the camera shops on Nathan Road are run by shysters who will give you the run around.
The usual scam is this, I want XYZ lens or camera.
I'm sorry sir bit we only have a display model, we can get you one in 24 hours if you want.
You come back in 24 hours sorry still not here, pay deposit can get it faster.
So you pay a deposit
You come back 1 of 4 things happens:
Do I know you? Deposit what deposit? Who the hell are you I don't know you , most tourists won't complain to the tourist board or know how to or have the time to go to trading standards or ICAC so they get ripped off.
Same as above but a big beefy guy will come out and pressure you into paying for it, once you've paid for it you open the box and find a brick or something inside a box.
You get low balled, i.e. they will offer you an amazing deal for a camera body lens or whatever but you can't buy the damned thing without buying 100+ accessories, they conveniently omit to tell you this until after you have the item in your hand, you don't buy they keep the deposit they lose nothing you leave HK upset.
To avoid this scam simply dont shop on Nathan road and only go to Fortress or Broadway, sure it costs a bit more but with no sales tax (VAT) and weak currency (comparatively) it will still end up cheaper. Oh and also DO your research before hand.