Received yesterday from a USA Ebay seller for £28 + £24 shipping, the most I've ever paid for a used flash but I've been looking for a 555 and a Pentax PT-1D interface adaptor. I already have three 455s (one non-working for spares) and a 544 - all similar hammerheads with GNs of over 40 metres. The shipping price is low compared with most USA to UK prices on Ebay..
This came with a simple PC sync lead as well as the Pentax adaptor lead (an EXT-11 I think). It works, with a nice low thud, and I have just measured the trigger voltage at 6.8v, about the same as a Pentax AF280T and it will be OK on my DSLR.
It is missing the camera (tripod socket) attachment screw, but I have the 455 spares. More significantly the slide switch just below the word "F/stop" is obviously not connected to anything - it just slides around even under gravity. It is supposed to select between the seven(!) Auto modes.
I'm not going to complain about the switch as I believe I can fix it. These panel switches connect to the real switches on a circuit board inside, usually by a little fork. Either that fork has broken, or more likely this has been taken apart for some reason and re-assembled without the fork engaging. I have had my 455s in pieces before now and it is very tricky to get all the several forks on the controls to engage when you re-assemble. The construction of this 555 looks very similar to the 455, it is basically the same unit with extra features.