Lets divide the tests to a few parts
First off, DO your homework on the quirks and issues of the camera in question. Next, ASK the owner about any perceived quirks about it, any cases of dropping, etc.
Try not to buy "project" or scrap cameras unless you know how to refurbish them or can get it at a very low price.
Now for the actual test. Take note the test is not exhausive and that many of the sections are really common sense.
Exterior
- Check for large dents at key components like the top of the camera near the rangefinder, near the lens/lens mount.
- Check for loose parts.
- Check for the functionality of the buttons/switches. (Especially that the camera WINDS properly)
- Check focusing (also see rangefinder/viewfinder)
- Check focus ring (if lens is included). This should be smooth throughout and not too loose/tight or jerky.
- Check that the aperture blades close properly and that no oil are present on them.
- Check that the lens mounts securely on and off.
- Check the condition of the glass, whether there be any haze, dust spots, oil on blades, etc.
Interior
- Check the film advance is working.
- Run a finger over the film guide rails. They should be smooth to the touch.
- Check that the spring back resists when you push against it and not be flat.
- If possible, run a scrap roll through and rewind while leaving the back open to see film advance and rewind is proper.
- Interior should be clean.
- Check light seals (if any).
- Check for obvious light leaks.
Rangfinder/Viewfinder
- Viewfinder should be clean and clear.
- Rangefinder spot should be easy to see and use.
- No misalignment of the vertical or horizontal alighment of the rangefinder.
- Framelines (if any) should be easy to see.
Shutter
If Cloth
- Check against a bright source of light for pinholes in the shutter cloth. Check once before you wind and after you wind the shutter.
- Check for cracks or wrinkling in the shutter material.
If Metal
- Check if metal blades are properly aligned and open and close easily with no collision when winding and firing the shutter
Shutter speeds for both.
- 1 sec - 1/60 should sound different from 1/60 - 1/1000 and beyond. Also, all speeds should sound slightly different from each other. More apparent on older cloth shuttered cameras. Metal shutters (except leaf bladed shutters) are usually quartz timed and are very accurate.
- at 1/500 - 1/1000, hold up to a bright light source and fire off shutter. You should perceive a sharp rectangle of light. If the rectangle has blurred edges, the shutter is capping at high speeds.
Hope this helps.
Samuel