You can reject in such case, just say, I appreciate

来源: 于 2007-09-19 14:22:03 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

the opportunity, but because xxx(your reason), I will have to pass the opportunity this time. Hope to work with you in the future.
No obligation. Nothing bad about it.