Considering a price guide, and would like additional input.
The Boston Pinball is based solely on Ebay sales (as is the Pinside guide as well I beleive)
The Mr Pinball guide seems to be the favorite.
I was looking at the Pinball Eric guide as well. One feature I like in this one is pricing for three grades. I beleive the Mr Pinball guide assumes collector grade and its the buyers work to figure out below that. Of course the ebay sales based guides don't take condition into account...but give a range to work from (with grade inferred, sorta). The ebay range I would think tends to be a bit broader because of those with more money than brains paying too much for a pin.