Don't get a camera that is too beat up. While Leicas can take a lot of abuse, one that has been obviously mistreated could require a total overhaul.
There are enough Leicas out there that you shouldn't have to buy someone's piece of crap.
I'm not a fan of photographers who toss their cameras about. Cameras are still precision equipment, and there'ss only so much that they can take before they break down.