I bought a (Parallel Import) Motorola V3 fairly cheaply from Shum Shui Po (meant to be cheap but lots of tourist traps if you're not careful). Catch: I knew exactly what I was getting and was fully aware of the following: No warranty (too bad if things go wrong after a quick check on the spot), no standard accessories (eg. handsfree kit removed but does have all essentials, ie. brand new battery, charger but with non-standard plug). Need to make sure you know EXACTLY what you'll get for an agreed price. After that I realize shopping malls in residential areas (where local people go) are much better with (reasonable) prices listed (mostly non-negotiable but at least you get a fair deal for what you pay).
Essentially all phones there are unlocked, new and used, even stolen phones as I heard