Which compensation method relies on a percentage of media buys?

The correct answer is the commission from media. This compensation method is specifically structured around earning a percentage based on the amount spent on media purchases. In this system, agencies receive a commission calculated as a percentage of the total media expenses incurred by their clients. This method aligns the interests of the agency and the client, as the agency benefits directly from the size of the media buy, incentivizing them to secure the best possible placements and rates for their clients.

In contrast, fee-based systems involve charging clients a flat fee for services rendered, independent of media expenses. Cost-based systems typically focus on covering the costs incurred while providing services rather than linking compensation to media spend. Incentive-based systems may involve bonuses or additional compensation linked to performance metrics, but don't specifically tie to media purchases directly. Hence, the distinctive characteristic of commission from media makes it the appropriate answer for this question.