What factor contributes to increasing an agent's player count?

The correct answer highlights the role of signing more players as a direct factor that contributes to increasing an agent's player count. Agents typically earn commissions based on the contracts they negotiate for their clients, which incentivizes them to continually seek out and sign new players. As they build their roster of athletes, their influence and earning potential within the industry grow.

Receiving an NBA salary does not inherently increase an agent's player count, as it refers to the earnings of a player rather than the activities of an agent in signing players. Similarly, while working with G-League teams can be beneficial for an agent’s career by showcasing their ability to scout and develop talent, it does not directly translate to an increase in player count unless it leads to new contracts. Coaching players focuses on training and developing the games of existing players rather than expanding the roster of clients an agent represents. Therefore, the action of signing more players is central to an agent's ability to grow their client base effectively.