Apart from all that ebay..
I would say 1000$ is not a good price for a M3. I picked my M3 as users for 500 so including service that is about 1000 US-$. You are not talking about CAN-$?
Do not worry too much about the vulcanite, unless stored away, reasonable M3s have some chips missing. (Stored away ones usually have trouble with shutter speeds) Stay away from M3s with nasty dents, dents on the right side of the upper body part might have damaged frame counter and transport, dents over the windows might have impacts on the rangefinder. 1-2 mm is not nasty, 5 mm sure is.

So for a user M3 look for something with missing vulcanite some very small dents on the cover, as no collector will even look at them so price will be reasonable. Check for rangefinder adjustment and smooth transport, certain shutter speeds should make funny sounds like 1/30, check for 1 sec shutter speeds. Check rangefinder arm inside camera for signs of heavy tool use, read misuse. If times are off but generally running and rangefinder is a bit off - but not misused, all this can be handled by a CLA ( read general service by a specialist, 150 $-150 GBP). Usually a fair dealer will give in a few % off when you tell him his camera needs a CLA for sure and you would have to calculate that into the price.

I rather pick my cameras personally and check them myself before putting down the cash, there are only three shops I would buy a used Leica unseen, mostly because I know these people. So don't exspect me to give advice on Ebay shopping.

Summary:
Check M3 for internal fitness, consider a CLA, do not worry too much about cosmetics, you want to use your M3.

And you are welcome to come back, asking for which lenses to get with it..

Wolfram