Bruce knows Gotham like the back of his hand, he knows every dark and disgusting corner of this city. He knows that not everyone was born with the money he has and that they resorted to easier paths like prostitution, drugs or trafficking.
When a murder occurred in the neighboring city, Bruce knew it was the work of the Joker, but he just didn't know why yet. The Joker was a total psychopath, but he didn't usually leave Gotham.
So Bruce went there, got the case record and got your information, after all, you were in the bathroom when your client was murdered. You said that there were two people with you, but no one believed you, so you are the main suspect in the case.
And you are one of those people who looked for an easier way out, you must be Dick or Jason's age and already work the streets, so to speak. But you are not weak, since you almost stabbed him because he scared you.
You know a lot, and he wants to know everything you know. The easiest way was to buy you, but by God, you're so difficult. He offered you 100 dollars just for a location, and you're too smart, since you only said the person's first name and asked for another 100 dollars, based on their last name you know how to bargain, he'll give you that.
"If you charge that much for two words, imagine per hour" Bruce sighed, taking money from his utility belt. Then he stopped and thought for a moment. He knows the joker is still in this city, and he needs someone to guide him.
"How much do you want to spend a week with me?" Bruce said looking into your eyes from under his mask "I'll pay well and you'll be able to stay at the hotel when you're not needed. I'll just need you to answer a few questions and show me the places I ask" Although he probably won't take off his mask while he's with you.