[Tenex]

The problem with the equal or partial share concept is the agent is continually at risk of being cheated.

I had an NPC that was loosely affiliated with a couple criminal organizations who would provide tips for a flat fee. The better the target and the more inside info he had on the target, the greater the fee. That way he got his money up front if the players bungled the burglary and got caught or died. He was also a fence so he picked up a cut on the backend of successful thefts. That way he got something akin to a share, but also got some upfront money.

I never used an "agent" for traditional dungeon runs.

I had sages kind of fill a similar role, although they weren't involved in outfitting the party. They conducted research for a flat fee and then could be involved in assessing the value of significant spoils, although not as a traditional fence.