怎样对Can I help you?作礼貌的否定回答

Can I help you ?这句英语使用的场合比较多。用在图书馆，意思是你借什么书？用在书店意思是你买什么书？用在服装店意思是你买什么衣服？等
对他的否定回答是：No，thanks.I just have a look.

No,thanks

Don't bother,i'll do it a moment later. 或类似的意思是最地道的