She is believed to have been drugged and transported in a bag to Borgial, an isolated village near Turin, before being released on 17 July, Italian police said.
It is claimed her captors released her without harming her or receiving any payment when they learned she has a child.
An online advert reported to have been published by a group called Black Death showed a photograph of Ms Ayling curled up with a calling card on her stomach offering “sexual services”.
It listed her details as: "Born in the UK; Abducted in Italy; Held in Germany; 19 year old; Caucasian; 34DD-25-35; Beginner model; Starting bid $300,000. Auction takes place 16.7.2017."
Italian newspaper Il Giornale reported Ms Ayling was told she would be sold outside of Europe.
“He [one of the alleged kidnappers] told me ... That he alone had earned more than €15m (£13.5m) in the last five years and explained to me that all the girls are destined for the Arab countries,” the paper reported she said.
“When the buyer gets tired of the girl bought by auction [they] can give them to other people, and when it is no longer of interest they are to become a ‘tiger meal’.”
In a statement, Ms Ayling described the moment she regained consciousness after being drugged.
“When I woke up I was wearing a pink bodysuit and the socks I am wearing now," she said.
“I realised I was in the boot of a car with my wrists and ankles handcuffed, adhesive tape on my mouth. I was inside a bag and was only able to breathe through a small hole.”
Investigators said they found a letter after searching a computer belonging to the gang, which read: “You are being released as a huge generosity from Black Death Group. Your release does, however, come with a warning and you should read this letter very carefully.
“You are certainly aware of your value on human slavery market and must make a note that this isn’t personal, this is business. For your release we have taken a number of factors into consideration.
“A mistake was made by capturing you, especially considering you are a young mother that should have in no circumstances be lured into kidnapping.
“Second important factor you are very well aware of is your overall protection by one of our main and very well respected men who made a very clear and solid stance in your case.
“You will, upon your landing in your home country cease any investigation activities related to your kidnapping. You also agreed to sneak a pre-determined set of information in to the media and we will expect to see evidence that has been done in the near future.
“You and your family will, in no way ever talk about us in bad language and without respect. You have been treated fairly, with respect and we expect to hear exactly the same about us in return.
“You can release any information you have heard from MO while your (sic) holding as he would never give you any information that could harm our activities.
“We will not tolerate lying about anything that has happened.
“You have also agreed to pay outstanding costs of your release of $50,000. We expect that money to be paid in BitCoins within one month.
“Any sort of disobedience with the above will result in your elimination.”
A Polish man, who lives in Britain, was arrested on 18 July on suspicion of kidnap and extortion, police said. Officials have released a mugshot of the suspect, named as 30-year-old Lukasz Pawel Herba.
It is alleged the men tried to sell Ms Ayling online for more than 300,000 dollars (£230,000) and demanded the model's agent pay to secure her safe release.
She was kept handcuffed to furniture but was freed after six days and taken to the British consulate in Milan, despite the ransom not being paid, police said.
It has been reported the captor demanded £50,000 upon her release and threatened to kill her if she told police about the incident.
Additional reporting by agencies