I know that Jineteros wait normally for tourists either at the entrance of the city or meet them at the bus station, or even approach them on the street. They may also just go inside buses and cars telling them that they are relatives (father, son, etc). They proceed telling them that the reservation at a specific casa has been cancelled or just that they are taking them to the booked casa particular, when in fact they are bringing you to a totally different casa.
If you have and trust your confirmed reservation at a casa particular, make sure you know the exact address, location and telephone number of the casa to avoid any unpleasant situation. And distrust those Jineteros that take you elsewhere.