As Jim Jones has mentioned, sellers do not always know about some of the problems with the cameras they are selling, or if they know, they tend to stay quiet about them. This is true of all old cameras. Fortunately Leica Barnack cameras are still repairable and serviceable, unlike many, many old cameras.
However, there are things you can do to conduct a quick and dirty assessment.
1- Check the lens by removing it from the camera and looking through it with a flashlight. Some dust or scratches on the front element are not a problem. A heavy haze can mean a cleaning is needed. Spider webbing or etching on the glass is a problem and may not be repairable. Deep scratching should be avoided as well though even this doesn't make the lens unusable.
2 - While the lens is off wind the shutter and check it. Looking at the top there is a lever on the right with A and R visible on the top plate. Make sure the lever is pointed at A. Wind the large knob on the right that has a skirt with numbers below it. This cocks the shutter and advances the film. While winding look through the hole where the lens was. A black curtain at the back will move. Watch for holes in the curtain and watch to see that the joint between the two curtains is together when it goes by. Once it is wound check that the front shutter dial is on "30" and then set the top shutter dial to 1000. The shutter should fire quickly with very little gap in the join point. Wind the shutter again and set the dial at 30 on the top dial. Press the button again. You should be able to see a definite gap between the two curtains as the shutter goes by. Now wind it again and, with the top dial still at "30", set the front dial to 2 or 1 and press the shutter button again. The shutter should fire, and there should be a definitive wait of approximately a second for the shutter to close again. You should also hear a buzzing noise. This is the delay mechanism and it should be smooth with no hesitation. Finally, wind the shutter once more. Return the front shutter dial to "30." Now rotate the top shutter dial to "B". When you press the shutter button this time, hold it down. Don't release it. The shutter should stay open for as long as you keep the shutter button held down. While the shutter is being held open, look at the metal piece behind it. That is the pressure plate and it should look smooth with no gouges or bad scratches. Release the button and let the shutter close.
3 - Now thread the lens back onto the camera. Pick the camera up and look through each of the two windows in the back. The one on the right gives you a view of the scene you are looking at. Though it is small it should provide a clear view. The one on the left will be magnified and is the one you will use to focus. Move the lens back and forth while looking though the left window. You should easily see a double image come and go as you turn the lens. If it is too blurry you will want to turn the lever underneath the lefthand knob until it gets clearer. If you still don't see a double image, or it is very, very faint, this could be a problem. If it is clear and easy to see then the rangefinder is in decent shape. Bringing the double image together in the rangefinder window is how you focus the camera. It is possible it will need adjustment but it will not need repair.
4 - That is about it. You can turn the camera over, turn the latch and pull off the bottom. Check that there is a spool on one side for loading your film.
If the camera passes all these tests then it will likely be a reliable workhorse. Outside appearance is secondary for me but it may be important to you. If so, be aware that these cameras had problems with chrome peeling off. In addition, the vulcanite (the black, leather looking covering) gets brittle and can start chipping away. None of this will effect how it works, but it may effect how you feel about the camera.
Good luck on Monday.