Blue Book Publications - https://store.bluebookinc.com/home/default.aspx
Vintage Guitar Price Guide - http://www.vintageguitar.com/priceguide/
Fret Not Guitar Repair - http://www.fretnotguitarrepair.com/company/instrument-appraisals.php
Pace Guitar Repair - http://www.paceguitarrepair.com/setup.html
Music and Arts - http://www.musicarts.com/MAC-Repairs-g20008t0.mac
Guitar Center - http://gc.guitarcenter.com/tradeup/index-10.cfm