I think Bob and Chris are both right here. KEH grades on cosmetics, their guaranty backs up function. All things being equal a piece of equipment that has been babied is likely to need a CLA less than one that has signs of heavy use, but let's be realistic. I have gotten plenty of good, useful stuff from KEH over the years and their BGN grade often applies to equipment that works great. BUT, my conclusion is that they don't necessarily thoroughly check out every piece of gear they buy. My guess is that they find it less expensive to address the complaints than to carefully go over the volume of used equipment they take in. That said, I would deal with them in a heartbeat as they have always made things right on the rare occasions when something needed attention.
Common sense: it depends on what you buy. If you are getting a 50 year old Rollei or Leica M or a 60 or 70 year old LTM Leica, you'd better budget a CLA whether the stuff is mint or not. A 50 year old camera with no signs of use may indeed have sat unused in a collection for decades. These are tools that need to be used and (like cars) will not function well if ignored for long periods of time. Lube dries out, cloth material ages etc., internal glass surfaces acquire deposits, dust and so on.
What dream camera inspired this question? At the risk of starting a flame war, not all cameras were created equal. If you were buying a used Nikon F3 or a Canon F1 it is a little different than buying a used Spotmatic (as much of a soft spot as I have for Pentax).
Ben Marks