感谢他们的聘请，告知不会接受，不必解释为什么不接受。接受与否是自己的事，与别人无关。（英文见内）

Dear Ms. Smith:

Thank you very much for offering me the XXX position in YYY company. After careful consideration, I regret that I have to decline your offer.

I enjoyed meeting you and the rest of your team. You have been most kind and gracious throughout the interview process, and I only wish that circumstances allowed me to accept your offer.

Best wishes for your continued success.

Sincerely,

John Smith