(OOC: As I thought, but just making sure. How much does a window cost, as an aside?)
"Good sir, I am a detective. Just as your heroic actions to protect our city feed your family, so too do my investigations help put bread on the table for me. I would be glad to tell you things that required a great deal of research, but first, please, you must hire me. Would you expect to receive no pay at all as a guard? Please, remember you did promise that to me before I came with you. I trust the honour and the justice of the Sharn Watch to continue as it always has as a shining example of integrity."
(OOC: The DC 15 Diplomacy check to raise Unfriendly to Indifferent (for that one guy) or Indifferent to Friendly (perhaps importantly, these new guards are listening too and might be affected also, which will subtly help) is trivial, particularly with Weapon's Aid Another)