Eddie, you seem confused about trade. When I deliver something of value to you and you respond by delivering something of value to me a transaction has occurred and we both benefited (hopefully). In the example you gave, the youtuber has something of value, his/her audience and they have worked hard to build that value. Gibson has something of value, a shiny new guitar that retails for $10,000 (and prolly costs them less than $500 to make). Youtuber and Gibson reach an agreement whereby said shiny new guitar goes to the Youtuber in exchange for a positive review/promo to the audience.

Did you really think Shaq uses Goldbond? Or that all those country legends gave two craps about whether their biscuits were made with Martha White flour?