We can understand that you are looking for an agency for getting "China Police Check", and you want an agency to make promise that you will get your China Police Check 100% sure.
But there are uncertain factors in the process of applying China Police Check, as municipal police of each Chinese city has its own protocals and rules in issuing Police Clearance Certificate. So the steps you took to get Beijing PCC successfully will not apply in Guangzhou city.
We are not a government agency/department, and we can not make decision for relevent Chinese government departments, such as Public Security Bureau (the Chinese counterpart of Western Police Bureau). But we will use our experience, knowledge and resource to obtain the China Police Check from the city you lived/living.
Note:
ChinaPoliceClearance.com can help in getting proof that a China PCC is unobtainable. This involves preparing a summary of the facts related to the applicant’s residence in China, immigration history, and employment or education in China, copies of related evidence, and an explanation for any evidence that has been stolen, lost, or mutilated; a summary of the national and local rules regarding issuance of police certificates and their notarization; description of our efforts to request that the relevant authorities accept and approve our application for the police certificates and notarization, with related evidence such as any application form; and a summary of the reasons why authorities were unwilling to accept the application or issue the police check certificate or notarize it, with any related evidence such as a written rejection notice or a summary of the reasons provided orally for the rejection.