Are they actually trusted to give independently good advice, or are they trusted to launder and expand on advice that leadership wants to hear but can't say themselves so that it can be plausibly deniable when it goes South? "We're mortified to discover that we allegedly did a bad thing, but in our defence we did specifically check with McKinsey and they said it was A-OK and so you can't actually blame us".
What if a CEO said, “We're mortified to discover that we allegedly did a bad thing, but in our defense we did specifically check with the ‘Charlie bit my finger’ kid and he said it was A-OK and so you can't actually blame us".
I don’t find McKinsey any more credible than a child sticking his fingers in the mouth of a baby who is surprised when he gets bit.
A consultant position should be one a person earns after spending 20 years in the industry, it is not something anyone should start out as.
I believe they try to project some of that earned trust to customers for the consulting side of the house. Though there is little, er, "accountability" for sign offs there.
If it pays off, the fee doesn't matter because we made more money. If it lost money, well we did our due diligence so we were just unfortunate.
It's both. There's some expectation that they aren't actively self-dealing... Besides the obvious expectation that they'd love to sell you further services. That's normal and expected, whereas them shilling for their other clients is not.