I agree with Steve, a working pro that truly relies on his equipment, as opposed to a well heeled amateur, will typically maintain his/her equipment regularly, and will make a point of telling you if you ask them.

I've owned several F4s through the years, everyone I bought that was from an amateur needed a CLA, without exception. The two that I bought from working pros (and they really showed it, looking "well used") performed flawlessly out of the box, and even with my reduced film usage, continue to.