With analogue equipment, everything revolves around mechanics that already have a lifetime behind them, and that is exactly where buying used through a vetted platform makes the difference. Every camera you find here has been professionally inspected and comes with at least 12 months' warranty, and you have a 14-day right of return. That way you know for certain that the shutter runs, the light meter is accurate and the seals are still doing their job before you shoot your first roll.
What should you look out for in a used analogue camera?
Check that the shutter speeds work smoothly across the whole range and that any built-in light meter still responds (it often needs a battery). On older bodies the light seals around the film door wear out — they are cheap to replace, but good to know about. With rangefinders, look for a bright, high-contrast viewfinder image and correct focusing, as with a Leica M6 TTL .72mm Silver or Contax T3. Medium format and large format systems consist of separate parts (body, film back, viewfinder, lens), so check which parts are included, especially with a Hasselblad 500C/M or Mamiya RZ67 Pro II.
Which type is for whom?
Popular models right now are the Fujifilm X half, fun for on the go, the Canon 1V HS, versatile and reliable, and the Contax T2, compact and discreet. If you are after maximum image quality for portrait, studio or landscape, medium format pays off with its larger negative; think of the Hasselblad 500C/M or Hasselblad 500 ELX. Large format cameras are there for the true enthusiast who wants full control over sharpness and perspective. Not sure? The Fujifilm X half is almost always the safest and most affordable start.