I am leaving for beijing tmr on package tour Been to beijing like 9 years back with a classmate. Ate some hawker food (at the food street) and after that my stomack was doing gymnastics. Anyway, even my beijing colleagues advised against me from eating hawker food, ie street side stuff. They say resturant prices are so cheap, no point risking it.
But if you are staying like a MONTH, maybe you can acclimatise you stomach to Beijing street fare. I going for 10 days, no time to risk it