打保票
Vouch for somebody.

【发音】dǎ bǎo piào

【释义】对某种结果事先作出保证。 
            Guarantee something before the result.

【例1】我敢打保票，他不是干那种事的人。
           I guarantee that he is not the type of person who would do such a thing.

【例2】我敢打保票， 我的消息很可靠。
           I can vouch for the accuracy of my information.