I've bought 6-8 boxes "full" in deals like this... 15% of list is a good rule of thumb but keep in mind craftsman and other oddball stuff are "give aways".. I always tend to ebay or post off here all the good stuff (Snap On, Matco, Mac, Cornwell) and if its something people want and the price is right it moves. If its an oddball brand its a hard sell unless you are giving it away. So make sure its full of top shelf tools and don't pay for broken old unwarrantiable/sellable stuff. Best rule of thumb is not to buy anything that isn't worth you yourself keeping. If you don't want it for your own collection its worth even less because you could get stuck with it.. and thats your $$/investment. Also air tools are worth about nothing used. A $400 Snap On gun brings $50-75 on ebay, etc. So generally I don't pay for air tools. If that makes sense? Either way.. try to base any calculations on complete matched sets and not loose misc ****. If you roll up and the guys box looks like a tornado hit it, RUN AWAY because there is a 99% chance you will end up with a bunch of broken up, mismatched, missing pieces, etc sets. I've learned the hard way sometimes. Also don't be afraid to make an offer.. cash talks.. have a truck/trailer ready to load the stuff and not have to "come back later" that gives the guy too much time to hem n haw about it and then you come back to find stuff cherry picked because "my brother wants that or I decided to keep that, etc" I've walked away from some boxes after viewing them only to be called back by the seller and saying "I'll take your offer" then you show up and 1/2 of everything is gone. Offers changed dude. Either way.. don't get caught up in the excitement. Its like buying an old crappy car.. do your research and take your time.