Further, he specifically mentioned Bordain, who focussed predominantly on food, and I think the concept of doing what the locals do is hugely rooted in choosing a restaurant. As in: locals won't eat in overpriced tourist traps, and will have had the chance to try enough local spots to know where's good. So if you want to choose a (e.g.) Chinese restaurant, choose one with lots of Chinese people in. (This applies whether you're in China or elsewhere.)

Well, it dépends: there are a lot of places where the locals goes because they are cheap not because they are good.

But yes, ask the locals.