It's a great camera, I have one sitting on my shelf. The 'standard' 80mm Planar lens is one of the sharpest ever made. The price sounds OK as long as its in good condition the 500c/m had a long production run the later cameras had a brighter focus screen.
With an A12 back (which is what I presume you mean by 'cassette") that can be swapped mid roll so you can take colour and B&W to the shoot made these cameras the SLR of choice for Pros.
NASA took Hasellblads to the moon so obviously they were trusted for Spacemen so why not Mr Spaceman?
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You can tell the age with the VHPICTURES codes on the body.
http://photonotes.org/cgi-bin/photo-entry.pl?id=VHPictures
Mark
I prefer my Rolleiflex as I'm a one lens guy, but if I was shooting studio portraits again a 'blad with 150mm lens is wonderful.