To assert or confirm as a result of one's own experience that something is true or accurately so described. I can vouch for his honesty because I've known him for years.
To give personal assurances or a guarantee. She vouched for the quality of the product, having used it herself.
To support or substantiate (a claim, account, or document) with evidence or detailed reference; to audit. During the audit, the accountant carefully vouched each entry with the original receipts.