How Many Shots?

Looking at a used 7D,Looks Good, But I wonder How Many shutter Clicks is has.Is there any way to Tell if it is Over or under used?

Well to put it simply, the 7D shutter is rated at 150,000 cycles, so you should look at how old the body is by age versus the number of clicks the body has on it. With that said, this only tells you about how the previous owner(s) used the body, and if anything the 150,000 cycle rating is not something set in stone per se. You could have a body with only 1,000 shutter count and have the shutter fail as well. Just use your best judgement

forget the rating, my 40D shutter died after some 30k shots, it's just a so so benchmark. But if you google 7D shutter count you'll find some ways to see it, with some software and a bit of work. You can't just see it on the menu of the camera on in the EXIF data.
Wait, actually for the 7D you might be able to upload a jpg to a website (forget the name, google will find it) and see it there, they charge a small fee. Like $3 or so.

If you can, look at the camera. are the buttons all worn, corners worn? Or does it look more like new out of the box? things like that.

Always a gamble, but if the price is right, might be worth it. New shutter cost me $250, so maybe calc that into your consideration. I'd guess 7D shutter is in the same ballpark

If you have the opportunity and the 7D has the latest firmware installed, format a CF card in the camera and put Magic Lantern on that card and run the camera's firmware update. The shutter count and live view actuations are shown in one of the menus brought up with the trashcan (delete) key.