Did your friend bring the handbag into Chanel for repairs? Only with repairs do the items get authenticated, otherwise Chanel does not authenticate handbags simply by drop-ins.There is a shop in Tsim Sha Tsui East called Tycoon city, it is right behind the DFS. They have all kinds of watches and handbags. The handbags in particular are cheaper than the actual retail stores.
There is also a building in Causeway Bay called Hang Lung Center. Go to the 13th or 14th floor and there are a few shops on the left that sell name brand products for cheaper. I think they are called Pastelli. I have seen BV bags for 40% off Hong Kong retail prices. These stores actually do a lot of wholesale to China but also have a large selection of regular clothes, shoes and bags to purchase. The only issue is that since they do wholesale their shops are a bit messy.
One of the most popular stores around is called Twist, they are a little more commercial. The shopping experience is a lot better than the ones in Hang Lung. They have decent prices but it won't be as cheap as the ones in Hang Lung Center.
I am 100% sure that their products are authentic because my friend bought a Chanel purse from Pastelli and brought it in to the Chanel store to check. Everything checked out fine.