The NY Times has a long article on sex slavery in the Islamic State, by Rukmini Callimachi, including some detail about the market's rules and institutional features:
ISIS Enshrines a Theology of Rape--Claiming the Quran’s support, the Islamic State codifies sex slavery in conquered regions of Iraq and Syria and uses the practice as a recruiting tool.
"The systematic rape of women and girls from the Yazidi religious minority has become deeply enmeshed in the organization and the radical theology of the Islamic State in the year since the group announced it was reviving slavery as an institution.
...
"The trade in Yazidi women and girls has created a persistent infrastructure, with a network of warehouses where the victims are held, viewing rooms where they are inspected and marketed, and a dedicated fleet of buses used to transport them.
...
"A growing body of internal policy memos and theological discussions has established guidelines for slavery, including a lengthy how-to manual issued by the Islamic State Research and Fatwa Department just last month.
...
"The Islamic State’s formal introduction of systematic sexual slavery dates to Aug. 3, 2014, when its fighters invaded the villages on the southern flank of Mount Sinjar, a craggy massif of dun-colored rock in northern Iraq.
...
"Their captors appeared to have a system in place, replete with its own methodology of inventorying the women, as well as their own lexicon. Women and girls were referred to as “Sabaya,” followed by their name. Some were bought by wholesalers, who photographed and gave them numbers, to advertise them to potential buyers.
"Osman Hassan Ali, a Yazidi businessman who has successfully smuggled out numerous Yazidi women, said he posed as a buyer in order to be sent the photographs. He shared a dozen images, each one showing a Yazidi woman sitting in a bare room on a couch, facing the camera with a blank, unsmiling expression. On the edge of the photograph is written in Arabic, “Sabaya No. 1,” “Sabaya No. 2,” and so on.
...
"The use of sex slavery by the Islamic State initially surprised even the group’s most ardent supporters, many of whom sparred with journalists online after the first reports of systematic rape."
...
"In a pamphlet published online in December, the Research and Fatwa Department of the Islamic State detailed best practices, including explaining that slaves belong to the estate of the fighter who bought them and therefore can be willed to another man and disposed of just like any other property after his death.
"Recent escapees describe an intricate bureaucracy surrounding their captivity, with their status as a slave registered in a contract. When their owner would sell them to another buyer, a new contract would be drafted, like transferring a property deed. At the same time, slaves can also be set free, and fighters are promised a heavenly reward for doing so.
"Though rare, this has created one avenue of escape for victims.
"A 25-year-old victim who escaped last month, identified by her first initial, A, described how one day her Libyan master handed her a laminated piece of paper. He explained that he had finished his training as a suicide bomber and was planning to blow himself up, and was therefore setting her free."
ISIS Enshrines a Theology of Rape--Claiming the Quran’s support, the Islamic State codifies sex slavery in conquered regions of Iraq and Syria and uses the practice as a recruiting tool.
"The systematic rape of women and girls from the Yazidi religious minority has become deeply enmeshed in the organization and the radical theology of the Islamic State in the year since the group announced it was reviving slavery as an institution.
...
"The trade in Yazidi women and girls has created a persistent infrastructure, with a network of warehouses where the victims are held, viewing rooms where they are inspected and marketed, and a dedicated fleet of buses used to transport them.
...
"A growing body of internal policy memos and theological discussions has established guidelines for slavery, including a lengthy how-to manual issued by the Islamic State Research and Fatwa Department just last month.
...
"The Islamic State’s formal introduction of systematic sexual slavery dates to Aug. 3, 2014, when its fighters invaded the villages on the southern flank of Mount Sinjar, a craggy massif of dun-colored rock in northern Iraq.
...
"Their captors appeared to have a system in place, replete with its own methodology of inventorying the women, as well as their own lexicon. Women and girls were referred to as “Sabaya,” followed by their name. Some were bought by wholesalers, who photographed and gave them numbers, to advertise them to potential buyers.
"Osman Hassan Ali, a Yazidi businessman who has successfully smuggled out numerous Yazidi women, said he posed as a buyer in order to be sent the photographs. He shared a dozen images, each one showing a Yazidi woman sitting in a bare room on a couch, facing the camera with a blank, unsmiling expression. On the edge of the photograph is written in Arabic, “Sabaya No. 1,” “Sabaya No. 2,” and so on.
...
"The use of sex slavery by the Islamic State initially surprised even the group’s most ardent supporters, many of whom sparred with journalists online after the first reports of systematic rape."
...
"In a pamphlet published online in December, the Research and Fatwa Department of the Islamic State detailed best practices, including explaining that slaves belong to the estate of the fighter who bought them and therefore can be willed to another man and disposed of just like any other property after his death.
"Recent escapees describe an intricate bureaucracy surrounding their captivity, with their status as a slave registered in a contract. When their owner would sell them to another buyer, a new contract would be drafted, like transferring a property deed. At the same time, slaves can also be set free, and fighters are promised a heavenly reward for doing so.
"Though rare, this has created one avenue of escape for victims.
"A 25-year-old victim who escaped last month, identified by her first initial, A, described how one day her Libyan master handed her a laminated piece of paper. He explained that he had finished his training as a suicide bomber and was planning to blow himself up, and was therefore setting her free."