First of all, you should buy diamonds from trusted merchants, because diamonds are not finished after they are bought. Merchants generally provide lifelong free services, such as regular cleaning, stone fixing (diamonds are easy to loosen with 950) and so on. If you are not a big brand merchant, you will not dare to put it back to change the number, let alone go to the roadside jewelry processing.
Besides, if a ring is made of a bare diamond, it's hard to tell the color of the diamond. The prices of diamonds of different colors vary greatly, so you should go to reputable businesses (Zhou Shengsheng and Chow Tai Fook are both good, and Xie Ruilin is too expensive and uneconomical, so it is not recommended).
China's Dai Mengde and Jun 'an are actually not bad. I don't know which city you are in. Jun 'an doesn't seem to be everywhere. Jun 'an is of good quality. I bought three diamond rings there.