Apart from differences between models like which lens is fitted, one of the main factors determining a value is a camera's condition. Collectors will pay top prices for cameras which are like new. And easily pay less than half when a camera looks tatty, is missing parts, or is defective.

Here's a checklist you can use to determine condition:

1. First look at the camera as a whole. Are there scratches, are there dents? Are parts missing, is there evidence it has been opened or repaired (look carefully if all screws are undamaged, and for signs the leatherette has been off to reach screws)

2. Then test if the shutter works at all speeds, especially the slower speeds like 1 second. A good test point is 1/10th of a second - it has a specific sound which will tell you if the shutter is off at that speed

3. For reflex cameras: check if the mirror flips up properly and isn't dull

4. Then point the camera at an object at a known distance and check if when focusing the distance shown on the camera corresponds with the actual distance

5. Check if there is no play, especially at a film transport handle and between the lens and the body (try to move the lens while holding the body fixed in your other hand)

6. Then check the lens. You don't want to see scratch marks or stains on the outside. Hold the lens to a light source like a light bulb and look through it. You don't want to see scratches, and internally you don't want to see obscurities or thin lines (fungus). Slight marks on the front of the lens are not so disastrous as marks on the back of the lens (inside the camera body)

7. Look on the inside of the camera for evidence of wear. Sometimes many rolls of film going through have caused a lot of wear. Shutter curtains may be damaged

8. For cameras with batteries: check the battery compartment. Leaking batteries could have caused a lot of damage

9. Check if the exposure meter works and gives a reading which makes sense in various light conditions.

To find how condition and other factors affect the value of a classic camera, there's a free guide "How to easily determine vintage camera values yourself" at http://www.vintage-camera-online.com.