via: https://www.themuse.com/advice/how-to-gracefully-turn-down-a-job-offer
A heartfelt—and specific—thank-you for that time and effort will go a long way.
The best approach is to be brief but honest about your specific reason for not accepting the position, saying something like:
Send a thank you note to everyone
Step 1: Show Your Appreciation
A heartfelt—and specific—thank-you for that time and effort will go a long way. Step 2: Give a Good, Brief Reason
The best approach is to be brief but honest about your specific reason for not accepting the position, saying something like:
Step 3: Stay in Touch
Send a thank you note to everyone