Part of the aura of ruleteros is that they are like Forrest Gump's box of choclates: "you never know what you gonna get." They could be medical doctors or lawyers that for one reason pr another decided to earn a living as ruleteros. Conversations with these guys can be amusing, as they will probably talk about how they ended up there. Other ruleteros are the more common street-philosopher type. Still, politics, traffic and panbol are great conversation topics. Check the example from the post dar en la torre o madre, where the ruletero is providing some deep insights to the passenger.
The word on the street is that some taximeters are tampered. So you should better have a good estimate of the cost of your ride. Otherwise you're at risk of being scammed. One has to be trucha or savvy.
Chafirete (cha-fee-REH-teh) is another word for ruletero and derives from the word chofer (lit. chauffeur). The word ruletero became a classic reference after Perez Prado's "Mambo del Ruletero." Check the video bellow from a movie of the 1950's.
Beware that sometimes hailing cabs on the street may not be safest for foreigners, or even provincianos.