Hiring a translation agency and recruiting an individual translator for Japanese translation services are both options with their own pros and cons.
Skilled teams of translators often utilize a Translation Management System (TMS) to manage their translation projects in the best way possible. A TMS is constructed to facilitate multi-person teams doing fast, good work on complicated translation processes, splitting up tasks while aiding communication to streamline the translation process. Translations commissioned from an individual translator can take longer on average since all of the workload is on one person. Translation agencies allow for an easier time bouncing work from person to person, meaning that it is possible for more work to be done on a specific translation task in a shorter period of time by using a TMS. A good translation agencies should also have already gone through the process of finding a good Japanese translator for a specific industry. For example, a translator that is knowledgeable about the law industry can be hard to find and it can be even harder when looking for Japanese translation services. An agency should already have searched, tested, and hired a great Japanese translator for a specific industry. If you work with a translation agency that you trust, it will cut out the task of finding good Japanese translation services.
When hiring an individual translator, however, one is interfacing directly with a specific individual who can be held accountable for quality, specifics of translation, etc. It's easier to have control over a project when working with individuals than it is with companies allowing for a more hands-on experience, if that is what you want. Though, a good translation company that you feel comfortable working with should accommodate any needs you have, including if you want more control on a project.
The upside to working with a translation agency is that they can get the best result for you without any hassle or extra work on your part. When working with an individual, without a TMS, there is no way to determine the quality because you only have one set of eyes on a project. When a translation team utilizes a TMS , translations go through several steps and revisions to ensure quality all while being much faster. In order for a good Japanese translation to be possible at all, a certain amount of personal innovation must be expressed, and translation is a job that requires no small amount of creativity, especially in certain types of texts. When it comes to Japanese translation services, Japanese and English are very dissimilar languages due to lacking common etymological roots, and Japanese is very nuanced in a few ways that English just isn't. Honorifics, choice of personal pronouns, and homophones possess potential for complexity as alien to an English speaker as it is obvious to a native Japanese speaker. A translation agency should have good Japanese translators on hand that understands industry specific terminology as well as an understanding of the two languages being questioned.
As is the case in many instances involving translation, the best option is often dependent on the individual translating task. Different translations, even between the same languages, and sometimes even when they're of similar general types, require very different skills and resources on the part of the translators in order to be done as well as they can be. The specialties of the individual translators and agencies that hire them will make or break how well a translation comes out. A book of one writer's haiku, for example, would likely benefit from the consistent voice, personal touch, availability for communication, and cumulative attention paid to a single project from hiring an individual translator. A compilation of technical instructions that needed to be available in the target language in a short period of time, by contrast, might be better entrusted to a translation service that could leverage the bulk of their resources to complete it in pieces, rapidly, with different subsets of the process going to individuals specializing in them within the service's teams.