The only "inspection" of a cedar shake roof I would accept is from a highly reputable roofing firm that specializes in cedar shake roofs. Other roofing contractors, and all other types of contractors in general, don't know when a shake roof needs to be replaced... they just make crap up and want to sell you a total roofing replacement job.
Where I live 80% of the shake roofs that have been replaced in the last five years did not need a $25,000 roof replacement, they needed a few bundles of shakes replaced and a good roof treatment for a total price of $1,500. By the way, a "Good" roof treatment for a shake roof does NOT include any pressure washing at all. The "Low Pressure, High Volume" claim of pressure washing a wood roof is a lie. Anytime someone pressure washes wood and the wood looks bright and fresh afterwards, the pressure stripped wood off the roofing. A person that is knowledgeable about wood roofs will refuse to let anyone with a pressure washer anywhere near their roof.