I have some very good advice on buying a pachinko(pa-chin-ko) machine/japaneese pinball.  If you are buying a new/fairly new machine just buy the machine there really are  no guidelines . But if you want a older model to play/restore this will help quite a bit.  Most of the machines will need at least a good cleaning. but if you want to restore a machine(probably the best choice for the machine) find a good restoration guide. But look for a few things. IT SHOULD BE COMPLETE there is a 1 out of 500 chance of finding a part  for sale individually so you should buy one with the most parts there. look for one thet has little to no rust dullness is fine but rust is very hard to slean up on the machines. If possible avoid getting one with water damage it eventually will rot the machine away which would result in rebuilding a whole new frame and backboard. easy way to say it too much work to do. basically get one with some dirt maybe needs glass replaced but with any major damage  it is not worth it.  also find one within your price range more than $100 shipped is too much for a restoration project.
if you want my opinion on a machine e-mail me through e-bay the item number and ill give you my opnion. IT WILL BE AN OPNION ONLY.