A 500 cm with dings? Stay away - there are a lot 500cm in a good shape! What budget do you have? If you want a reliable - then get one from a shop with warranty. For a first setup you should get a 500 cm and not only a "C" and not a 500 Elm or some of the other motorized Hasselblads. (and of cource you can still buy the big Hasselblad batteries) - outdoors its much nicer to work without a motor - and you can go out in cold weather without the camera failing. A 500 ElM for me is too heavy - I use mine mostly indoors. And a 50 as a Standardlens is also very inconvenient - if you want to get hocked with the great system - buy a 500cm with WLF, back and 80 - and if you can get a CF as a lens - that would be it. Be sure, that you can return the camera - 8 out of my 10 backs I bought used had issues that needed repair! Try the lens - look against strong light if the lens is clear - and then try the long times if they work (the other times should work too, of cource) - get an optech strap for Hasselblad if you shout outside for convenience. A Hasselbald is a great camera. I love the images but going outside - for me its too heavy - but I'm getting old too. I sell my 500 cm but keep my 500 ELX for indoor shouting, wouldn't want to miss it at the whole.
Keep patient - don't buy the first one you see!!! If you are not bathing in money you might want to wait a little - a beaten up Hasselbald is cheap and easy to find but often not a delight to use. You have to calculate some repair if you go with old stuff - and a Hassy is not as easy to be repaired as other cameras might be. If you have about 700 - 900 Euros - then you will have a good chance, if not: wait and save money!!!
Good luck - Frank