This is my first post after browsing around here for ages, but since I had this problem with a clients website before, I thought I might be able to help out.

Since the listing is of your clients address what you can do is
1. Click on the listing to open it in Google Maps
2. Click "more info" and then "Add or edit your business"
3. Choose "suspend this listing"

Google will send the infamous postcard to your client because their address is listed. After verifying the listing will be removed immediately. This worked for me so I hope it helps.