He sells food and beds. He will buy stolen goods from any character (even characters who are not in the Thieves Guild). He will refuse to do business with the Hero, or even talk with them, if his disposition is below 30.
Manheim runs the Inn that Rufio is staying in. When asked, he will offer up what he knows about Rufio, and how he keeps to himself.
Rufio: "Rufio? He's an old codger. Been living here for a couple weeks now. If you ask me, he's hiding from something. But what do I care? He pays his tab. His room is downstairs, in what I like to call the Private Quarters. Use that hatch in the floor over there. But don't expect a warm reception."