You can always haggle, they'll always go lower. I only buy jewellery down there now and tend to buy stuff that isn't on the high street here or that Topshop are selling for 3 times the price.
They all pretty much sell the same stuff to be honest. There's one lady who sells really nice jewellery pieces who I always go to now and she actually remembered me in May from my December visit, but I can't really describe where she is on the street. She's in the middle. See that helped, didn't it?!
The quality of the fake bags are crap to be honest. I bought a fake Gucci wallet and D&G bag the very first time I went to NYC in Summer 07 that both fell apart within 6 weeks. If you don't mind then go for it, but I'd rather just save my money for something that'll last longer than the flight home these days.
Canal Street's good for buying pressies for friends and fam back home. Have fun