(Adapted from Harvard Law School's 1998-1999 Public Interest Job Search Guide)
Even good employers have to be turned down sometimes. Whether you want to work in a different city, the employer cannot pay you enough, or you simply received a more attractive offer, you may find yourself in a situation where you need to reject an offer.
Always make an effort to turn down your employer without burning any bridges; it may be well worth it. Remember, you may find yourself looking for a job with the same employer, or hoping to make a networking contact through someone from the office with whom you really made a connection while interviewing. Just because you will not be working there for now, do not assume you will never be in touch with the office again.
First of all, keep your promises. If you had said you would call the employer with your answer by a certain date, do so. Always contact the person who offered you the job directly to let him/her know what your decision is.
Never leave a rejection on voice mail or with an assistant unless you have been instructed to do so. Make sure to thank the employer for his/her time, and offer an explanation for your refusal. Always follow up on your final conversation with a letter. If you are still interested in working for the organization in the future, leave the option open by noting in the letter or conversation that you will contact the organization during your next job search.