I see many use the pinball pricing guide. This can be misleading and the prices are understated when prices are trending up (i.e. it was advantageous to use the 2013 pricing guide when you bought pinball machines in early 2013 at the "top of the market" because the data is old so you get better pricing). HOWEVER, the 2014 pricing guide in my opinion is way overstated on MANY TITLES. So beware. Prices have come down on many titles since the book was put together (used date from late 2012 through mid 2013 which was "at the top of the market").
So be careful using pricing guides....plus condition is king and condition drives price more then anything. A players condition machine can be below the pricing guide and you can be getting "ripped off" or you may be buying a Chris Hutchins restored game for slightly above the pricing guide.....IN THAT CASE YOU ARE GETTING A GREAT DEAL !!!
So the pinball pricing guide is just that. Your best bet is to look for what machines sold for currently. SELLING PRICE not asking price and how long they sat before they sold....that is what I do.
Good luck to you !!!