first-hand

to show off one's special abilities or exhibit one's skills, often to impress others

to have an illicit romantic or sexual relationship with someone

to deliberately withhold essential knowledge or skills as strategic insurance (typically to maintain leverage, avoid being replaced, or preserve authority in hierarchical relationships)

to hide the truth from the masses or manipulate a situation using one's power

to take care of a matter all by oneself or to run the whole show

a transaction where payment and delivery of goods occur at the same time to ensure a direct and fair deal without reliance on credit