Any clerk at any pawn shop (around here) will whip out a calculator and give you exactly 8-10% off the top upon request.  the owner/mgr will do more.  I don't do pawnshops much anymore but when in HS/College I did a lot with guitars and amps.  On the stuff I know the values of - games, stereo, guitar/amp, tools - pawnshop tag prices around here are way high across the board.  i.e. a new circular saw costs 150, their price for the same well used tool is $115.  They are expecting to give some ground.  
**pawnbroker laws and styles do differ from region to region.  
$200 at 33% off tag price, for that sit-down cab, working, is obviously a smokin' deal, esp. with game board.  I don't follow candy cabs (basically non-existent on the East coast) but I know enough to know that equation works.