Glengarry Glen Ross
Let's get one thing clear right up front: Ricky Roma doesn't fit the role of the typical guide or mentor. He's not going to hand you your father's lightsaber or teach you how to defeat a dementor or anything. However, in the pursuit of the sale, he does put on the guise of a mentor when talking to Lingk, dropping life lessons like he's a Morgan Freeman voiceover:
ROMA: And what is it that we're afraid of? Loss. What else? (Pause.) The bank closes. We get sick, my wife died on a plane, the stock market collapsed […]What does it mean? I'm not secure. How can I be secure? (1.3.41-47)
Roma lays this kind of stuff down on Lingk throughout their first scene, and he goes back to bold life lessons when he's trying to hold on to the sale after Lingk wants to cancel it. In other words, guide/mentor is just one of many hats that Ricky Roma, super slick salesman, can step into to sway a potential buyer into purchasing.