The unidentified 20-year-old was injected in the arm with the tranquiliser ketamine after going to what was a fake photo shoot at a venue near Milan's central station on July 11.
The remote farmhouse where the model was held captive.
It is thought she was kept in the bag for two-and-a-half hours and stayed in Turin for six days.
The websites for the auctions included a description of the victim and a starting price but police said it was still unclear whether the suspect had made them up.
Italian police say the offender demanded €50,000 to free her and "threatened to kill her" if she told officers what happened to her.
"You have a two-year-old child and our rules exclude mothers", the kidnapper allegedly told her according to the Italian report. It is unclear if she attempted to gather the money.
A British model was abducted in Milan and put up for auction online after being lured to a sham photoshoot.
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He claimed he was working on behalf of the "Black Death" group - a deep web trafficking organization. The 20-year-old has given statements to police.
According to court documents, the woman was drugged by her abductor and held in a small town in the north-western Piedmont region of Italy.
The kidnapper used an encrypted account to ask the model's agent for £230,000 ($300,000) to stop her from being sold in auction.
Officers went through Herba's phone and computer and said they found photos of the woman and material stating she was for sale, while hair from both the model and Herba was found in the boot of his auto. It is now unclear why the kidnapping came to an end.
The woman was released after being held for six days and investigations are being carried out by authorities in Italy, Poland and the UK.
The woman's modelling agency then contacted police and Herba reportedly negotiated a ransom for about USD$60,000 ($75,000) with them.
A spokesperson for the Foreign Office confirmed they are "providing consular support to a British woman in Italy and are in touch with local authorities".