In my own experience interviewing people about systems they have worked on (as opposed to hypothetical on-the-spot design), we have been highly successful in routing out charlatans, as you put it. They very rapidly get hand-wavy and are only able to give the most shallow of answers. In a few cases they will go in-depth, but reveal truly bizarre decisions or lack of understanding of the platform.

Good senior engineers can usually go fairly deep, they are honest about where they don't have as much knowledge, and are usually candid about what was good and maybe what in retrospect was a hack or a bad decision in retrospect.