When it comes to discussing someone who "knows the ins and outs," there are a number of synonyms that can be used. Some other ways to describe an individual who is extremely knowledgeable and familiar with all the details and intricacies of a subject or situation include "an expert," "a specialist," "a seasoned professional," "a master," "a connoisseur," "a guru," "a virtuoso," "a secret weapon," or even simply "a pro." Regardless of which term is employed, the idea remains the same: this person has dedicated themselves to becoming an authority on the matter at hand, and is able to navigate even the most complex of challenges with ease.