Different agencies hire their translators on varying standards.

There are several details that will help you in ensuring this. One of these is to carefully consider the qualifications of the translators that will be working on your document.
Different agencies hire their translators on varying standards.
The most important factor that you will need to pay attention to when choosing a translation agency is the quality of the Japanese translation services. Everything else is secondary.
Find out what these are. Your focus should be on translators who have had some native experience with Japanese Chinese translation. Choosing a translator whose mother tongue is Japanese will go a long way in ensuring the fluency of the final result.
You should also pay attention to the experience of the translator. How long have they worked as translators and in what other capacities have they served outside the lingual field? For instance, a translator who served in some capacity within the legal translation will be able to handle legal Japanese translations more efficiently. The first will ensure that they are familiar with the rules behind Japanese translation while the latter will give them an edge if you require technical translation in a related field.