I was in ChengDu in August, and went to the one next to my hotel. The 技師 told me it's a chain-store/franchaise, and there's a few hundred nationwide. The store I went to is clean and attitude of staffs were nice. And that's right, they don't accept tip. In fact, I think most places outside of ShenZhen do not accept tip. I was in CheungSha in April, and went to a massage place. The service and skill of the 技師 was so good that I wanted to tip her, but she declined.
