In Prague I bought an old Flexaret IV, a twin-lens reflex camera from the 1960's. I was very happy with it, until it gave a short "click" even with a shutter speed of 1 sec. The shutter refused to open! When I developed the film it was clear that when I bought the camera it was still in working condition, and it had also survived the trip back to Amsterdam. After some messing about with a screwdriver and the moving bits of the camera I found out that the self-timer was stuck. Moving some pins around got it un-stuck, and so I have a working camera once again!
The camera refuses to work when it is closed but has no film in it. One thing I figured out while toying with it, was that it does work properly without film when the back has been opened. So if you're unsure whether to buy such a camera and you want to give it a try without wasting film, just open the back.