Engagement with your translation provider is the key to verifying whether the people doing your translations have these skills. But substantial engagement with a bulk translation seller is virtually impossible.
Many aspects of what happens to your documents after you order translations of them remain purposefully hidden from your sight but can affect accuracy, accountability, and security.
Japanese-to-English translators with neither Japanese nor English as a native language can look forward in the near future to replacement by machine translation systems suffering from the same handicap.
One troublesome characteristic of the Japanese language is the uncertainty of how Japanese personal names are pronounced. Many names can be pronounced in numerous ways, the pronunciation options sometimes being totally different.