Put in the date you're adding the note, ask the user to contact you because you can't find any problems and need help to fix it. Give them contact methods for you, such as email or a link to create a PM to you on the forums.
This is my boilerplate text for something like this:<pre>
Thank you for the map error report!
After checking all the roads in the area and comparing them against aerial photos, I am still unable to find a problem near by. Forward this email to firstname.lastname@example.org with your comments and additional information about this error report.
Please reply within 7 days so that the map may be updated quickly. If you cannot reply within that time, this request may be closed.
-The latest Waze downloads, information and community forums are at http://www.waze.com
-Interested in joining the community of map editors at Waze? head over to waze.com and get started. Editing manual is available in the wiki.
Alan A, OR Area Manager
The <pre> tags format the email such that all the line breaks are included. However, it also makes the text smaller and changes it to a different font. I've received more responses lately to update requests feedback than before, mostly from newer users. I still get maybe a 5% response rate.
I use Google Reader for my area/state and I star the ones I respond to so I remember to close them after 7 days.
There is more on this topic over in this thread