Faolyn
(she/her)
At this point I have to assume you never actually read anything I wrote, because I've addressed this.and you considered it the least important part because what mattered was to get the message to the contact, no matter how.
So how is the PC not finding the messenger or the messenger refusing not an issue then? Do they try again until they succeed? Then why even bother with letting them fail once if you ultimately guarantee delivery anyway and all that changes is the number of hoops they had to jump through…
I am not taking away player agency by point-blank saying they can't try to roll to find a messenger. That's what you are doing by flat-out saying the ability doesn't work.
If they roll for it (or roleplay it out) and fail, then it's no different than if they roll to pick a lock a fail--they can't try again right then and there.
Maybe they can try again tomorrow: "Sorry, you don't see anyone in the bar with a tattoo that indicates an association with the Guild Of Thieves, Lowlifes, and Affiliated Scum. You can try again tomorrow night."
Maybe they can't try again in this area: "You've learned that the guards are really cracking down on crime in this town. All those gibbets hanging from the town walls you saw when you came in? Yeah. Anyone in this town who could have passed your message along has fled or is lying low. You can try to find a messenger in the next town."
Or maybe they actually can try again right away, but only if they figure out a completely different approach: "Based on your rolls and your painstaking research, you've discovered that the town that I described as being in the middle of the grasslands in fact has no docks and therefore has no seedy sailors. Did you want to try looking somewhere else?"
(These, of course, are examples and are certainly not exhaustive.)
But any of these are better than just flat-out saying "no, this doesn't work."