Second the old lenses and film holder warning. However, an used film holder with leaks can be fixed with gaffers tape and black acrylic paint most of the time. The only time a film holder is completely shot is when the top leaks. Same thing for the bellows on the camera, gaffers tape and black paint can be a great fix. Also, easiest way to check the bellows is at night in complete darkness with a flash light in side of the camera. Great way to spot leaks. Film holders can be checked a similar way, just not as effective.
The shutters on the lenses are what I would be most concerned with. Older lenses that have not been fired in a while and left in the same position tend to have the lubricant in the shutters gum up in a certain position (just like how a refrigerator that is left on its side for a while needs to stand upright for a day before plugging it in). This will then lead the lube to spray when fired for the first time again; this can lead to serious problems.
Also, many people do not know how to use a Copal shutter (or similar manual leaf shutter) and therefore do not know how to properly rank the shutter when selling. I ran into this recently and bought a used lens with a bad shutter that was labeled as working perfectly fine. Fortunately I am familiar with Copal shutters and realized it was not working properly when I received it; I sent it back. If you buy off of ebay, I recommend that you find someone who is familiar with Copal shutters to test the lens and make sure it is working. Also, when you receive the lens, make sure to unscrew it so you can make sure there are no marks any were on the glass.
On testing the lens, I was once told by a older and much more seasoned photographer, "do you have a girlfriend? Good, have her lay down on your bed in a pair of panty hose. If you can focus on her legs with a loop and see the stitching on the ground glass, then you know you have a sharp lens."