If only a patent certificate is needed, any institution can do it. If you consider safeguarding rights, you'd better spend more money to choose a formal agency, which can provide you with full service.
The level of patent agent can directly affect the value of your patent. (If the examination and approval of a patent for utility model does not require substantive examination, it can generally be authorized. If you use it to protect rights, others can invalidate your patent and so on. )
For regular institutions in Beijing, you can check it on the website of China National Intellectual Property Administration.
Beijing is really 3500, so consider the agent in Shenzhen.
The number of formal intermediaries in Shenzhen is around 2,500 (including application fees and agency fees).