Are you willing to vouch for him?

你愿意为他担保吗？

《牛津词典》

Kim's mother agreed to vouch for Maria and get her a job.

金的母亲同意为玛丽亚担保，好让她找到一份工作。

《柯林斯英汉双解大词典》

I can vouch for her ability to work hard.

我保证她能够努力工作。

《牛津词典》

In return for American help with China's access to the World Trade Organization, Beijing would vouch to provide unprecedented business opportunities for U.S. multinationals.

CNN: Jiang keen to ensure U.S. relations not damaged

W. Bush to vouch for its commitment to ideas over party.

FORBES: Magazine Article

Is there really no one from Cranbrook that Romney can persuade to vouch for him?

FORBES: Bullying and Mitt Romney's Empathy Problem