From the blog "Slavers Of Skyrim Devlopment Blog"

The fallowing writing is a draft that goign to change a lot before made it reality. its a recording of this moment how things look. its possible goign to droped as designing happening.   i thinking this: when player OR player follower OR any special character got captured logical step frol slaver guild send a spcialized trainer to train the new slave.   Thistrainer tasked to brake in the slave so slaver guild can ask more price for the slave when sold one of it clients.