Employment Verification?

Here is a transcript of a message that was left on my voicemail today:

Hello, ummmm... I'm trying to reach (company name redacted), um, and I hope to make an employment verification for Michael (last name redacted). If you could please give me a call back at 1-800-xxx-xxxx, my extension is 604. Thank you so much.

When I first got my telephone number many years ago, I soon found out that it was a recycled number, formerly belonging to some sort of software company. I often receive calls from business telemarketers trying to sell services and supplies to this company. God damn those annoying telemarketers! I have tried to find out as much about it as I can about this company, but the telemarketers don't know anything about it except that it shows up in a database of businesses. Now I have a caller who is inquiring about a former employee. Maybe it's time for me to get some payback from one of the people who worked for this company that has caused me so many irritating telemarketer calls:

Yes, hello, my name is Johnny Introvert from (company name redacted) returning your call in regard to Michael (last name redacted). I am the founder and proprietor of this company, and I feel morally obligated to inform you that of all the people I have ever hired, Michael was the biggest mistake I've ever made. Two months after hiring him, I discovered that a large part of his resume was fraudulent. And understandably so--the guy was a walking disaster. Everything he touched broke within a matter of minutes. His incompetence and negligence easily cost the company tens if not hundreds of thousands of dollars. It took us a full year to fix everything he broke, and he was only with us for three months. If you are seriously thinking about hiring him, the only advice I can give is: don't!

Anyone have any other suggestions for how to respond?