Reliability of providers
As already explained, the translation industry is under-regulated, a situation which encourages the proliferation of so-called professionals who are only translators in name.
Therefore, we cannot stress enough the importance of checking the quality of a service provider's translations at the beginning of your business relationship (or have it checked, if you are unable to do so yourself). If the quality is good, you can rest easy in your choice. If not, you will know you need to look elsewhere.
Lastly, you should be aware that a service provider (whether it be an agency or a company) may be excellent in certain language combinations and decidedly less so in others. In this case also you should stay vigilant and not jump to any conclusions.