You have to wonder what the thought process is when an organization expressly prohibits their players from guesting for any other teams/orgs yet is constantly bringing in guest players and taking playing time away from those very same kids who pay the fees and go to every practice.
The process in our org was quite simple. If a team was in need of a pickup player, we looked internally first. My DD would often play up an age bracket as a pickup player, and we offered the same opportunity to other players in our org that we believed were ready. If that option wasn't available for a particular weekend, we would ask someone with history within our org or team. Perhaps someone that continues to play high school ball but didn't want to travel for tournaments during the summer. Only after those avenues were depleted would we ask someone from outside the organization. In most cases it was someone that approached us and expressed interest in our org.
I also don't understand teams/orgs that do not allow their players to pick up. Sure there needs to be some common sense applied, but it's harmless otherwise. If the fear is that another team is going to "steal" away the player, I doubt holding them hostage is going to prevent it in the long run.