I find this thread on the old site :
http://forums.webhelpdesk.com/forums/comments.php?DiscussionID=1545&page=1#Item_0
I can see where you can allow the client to do this by changing the label. My questions are:
1. Will the client get an email saying it is closed? We need this because we want them to fill out the survey
2. Will the tech see anything, will they get an email?
We just want to reduce complexity/confusing by allowing a client to close their ticket if they want to.