Language is already imprecise, and the tendency of the average person to omit, alter, or embellish the words of another is well known. It doesn't take much contemplation to reach the conclusion that the ability to communicate clearly is not as common as is often assumed, especially when it comes to conveying complex concepts or technical or specialized language. Friends, acquaintances, and especially employees often tend to overstate their abilities and understate their shortcomings -- people don't like to disappoint someone they know. It can be unsettling to think that the more unrealistic a person's sense of their own abilities the more likely they are to feel the need to make a display of them, perhaps seen as a momentous opportunity to do something different, exciting, or important. The question is: can risking your critical business or legal communications on a non-professional be worth the incidental savings? Probably not. Hiring a professional interpreter is the only way these problems can be avoided with any reasonable degree of confidence.

• The wording and meaning of what is said is to be followed as closely as linguistically possible.
  
  
• Nothing is to be unnecessarily added or omitted.
  
  
• Mastery of, or at least familiarization with, vocabulary appropriate to the task is completed in advance.
  
  
• The ability to interpret consecutively or simultaneously is required.
  
  
• Professionally appropriate timeliness, manners, and dress standards are followed.