In Shanghai there are bike shops everywhere, but then again there are bicycles everywhere so I guess that's no surprise. When I was last there I deliberately sought out some of the better ones but regular shops providing parts and servicing for commuter and work bikes are easy to find. When there's major work to do it just spills out on to the pavement, like most Chinese shops.
What is surprising is that there are more specialist shops too. I found a cool 'fixie' shop based in a typically basic and run down Chinese establishment.
Then there are outlets for a lot of the big global marques and I visited the Specialized, Trek and Giant stores.