There are certainly many of such businessmen (actually they're
just sales staff, usually) in singapore and admittedly, they will
do anything to "cheat" tourists.
However, one thing I must mention to you, while you're seeking
justice, is that, for future reference, perhaps you would like to
do some research on your intended purchase, especially expensive
equipment like cameras and audio/visual stuff.
It's no good walking into a shop just wanting a "camera". That's
when they will kick your ass silly (esp at sim lim) and u will end
up with what u are now. i'm not saying it's ur fault and that the
singaporean vendor is just doing his "job", i'm saying this
experience could have been avoided if u had certain product
knowledge of what u intend to spend hundreds of dollars on.