Obviuosly you have a "little used" M2. The take up spool is otherwise a good indicator. If there is heavy brassing at the entrance to the flat spring that holds the film, you know that it has been used a lot. Very often you can find new dials and take-up spools installed to "raise" the value. It used to be easy to find these items, but now a new dial will set you back $100+ and the spool about $40 so most sellers dont bother anymore.
The eyelet for the strap is also a good indicator, if there is heavy wear in them, it i reasonable to assume that it has been used a lot. Of course the finder should be clear and no little specks (caused by the blackening compund used for the finder assembly flaking off) and the focussing patch should be clear and well defined.
The edge of the film counter dial will also show wear on heavy users, you can see brassing showing through the chrome as well at the surface of the top-plate just at the rewind knob. Of course often you have the typical scratches from the MR Meter, but that usually indicates that it was used by an amateaur rather than a pro.
The advance should be smooth, with no mechanical sound (almost sounds like it is gritty) although that is something that any used M can have prior to a CLA.
Also check the back plate - are the two little rubber stops at the top corners intact. Flip the back door open and remove the lens and cycle through all the speeds (put your eye right at the shutter opening and aim the camera at a bright light source and trigger the shutter. You wont be able to tell if the speeds are dead on, but you can check that the curtains are opening properly, you should be able to "spot" the light even at 1/1000. At the slow speeds check that the curtains travel across the opening wih a even speed. Also look at the 2nd curtain when it stops at the end of its travel. On the leding edge of the curtain, there is a metal bar (it holds the curtain straight vertically as well as provides the attachment for the "straps" or "tapes" that are attached to the shutter drum. If you can see this bar at the left (from the back) when the shutter has stopped, the shutter needs adjustment. The shutter blinds should be evenly colored black and smooth. If there is discolored patches or wrinkles it is probably at the end of its usefulness and needs replacement. The shutter cloth also tends to "stiffen" with age and can show small cracks.
None of this is bad, but it is something to take into consideration when you are looking at a used M. It can all be fixed - but at a price. If the finder is "shot' you might not want to deal with it as that will set you back $3-400, but most everything else can be fixed with a CLA and even a shutter blind replacement can be a good deal if the camera is cheap enough. The good thing is that once the CLA is done and you keep using the camera, it should last a long time!
Cosmetics never bothered me as long as it works perfect. Mintish cameras scare me as " where has this camera been for the last 40+ years?". Often you get heftier repair bills for the mint cameras, because everything is dried out. The well used and well kept camera is a better deal, unless you are a collector.
