Mike is a forward-thinking appraiser with some ideas about Customary and Reasonable.  Perhaps we need to retire the word "Customary" and just go with "Reasonable."  Further, he has written about how to determine Reasonable in a way that is... well... pretty reasonable.  

http://appraisersblogs.com/appraisal/free-enterprise-an-appraisal-myth/

http://mfford.com/html/c___r_fees.htm