Why is there such a discrepancy between used car prices quoted by NADA
(nadaguides.com), Edmunds True Market Value (edmunds.com) and Kelley
Blue Book (kbb.com)?  For instance - for zip-code 98908 a used 2001
Toyota Highlander (limited)with 50,000 miles and in good condition,
with no additional options, has trade-in values of $15,655, $18,328
and $20,750 respectively from kbb, edmunds, and nada - and that is a
range greater than $5000.  Quoted retail values for the same vehicle
are $21,380, $19,901 (or $20,901 if "certified") and $23,925
respectively from the same three entities - and that is a range
greater than $4,000.  Which of these guidelines is most reliable and
credible?  In searching the Internet I could not find an article that
dealt with my question.