Those guides are a joke. They are rarely close, and usually very low, or very high. They tend to pump up the ego's of those certain clowns who think their cars will sell for those inflated Barrett Jackson type values.
__________________
1976 LeMans B09 Freeway Enforcer, 455/M40 Smokey
1977 Trans Am, 400/M21 Black/Gold Bandit. 44K actual miles
2017 Sierra SLT 1500 Z71 4X4
2019 Canyon SLT Crew 4X4