Apparently it's hard to staff a really high volume brothel entirely with voluntary sex workers. The Guardian has the story:
Trouble in Paradise: the rise and fall of Germany's 'brothel king'
Jürgen Rudloff’s chain of ‘wellness spas’ sold sex as a health service for men. But his business model was fatally flawed – as his trial for aiding and abetting trafficking revealed
"Until his dramatic fall from grace, Jürgen Rudloff was the self-proclaimed “brothel king” of Germany. Owner of a chain of clubs he boasted was the “the largest marketplace for sex in Europe”, he was every inch the well-dressed entrepreneur, a regular face on reality TV and chat shows.
"Rudloff is now serving a five-year sentence for aiding and abetting trafficking. His trial laid bare the misery and abuse of women working as prostitutes at his club who, according to court documents, were treated like animals and beaten if they didn’t make enough money. His imprisonment has dismantled the idea of Germany’s “clean prostitution” industry and raised troubling questions about what lies behind the legalised, booming sex trade.
"Prostitution – legalised in Germany in 2002 – is worth an annual €15bn (£13.4bn), and more than a million men visit prostitutes every day. The change in the law led to a rise in “super brothels”, attracting tourists from countries where such establishments are illegal.
...
"The Paradise business model is the same as the hundreds of other “sauna clubs” across Germany – brothel owners provide the premises, and the women are self-employed. Yet Rudloff’s high-volume, low-cost model only works if the supply of women is enough to satisfy demand and bring enough customers through the doors.
"According to court documents, this became a problem for Paradise almost immediately. There weren’t enough women to fill the clubs. So Rudloff’s friends in the industry offered to help him out.
"In 2008, as Rudloff was growing his business, investigators in Augsburg, Bavaria – a hundred miles from Stuttgart – received a tip-off that gangs from the city were trafficking women from eastern Europe, and sending them to work in Paradise. (While prostitution is legal in Germany, pimping and sex trafficking are not.)
...
"Peter Holzwarth, the chief prosecutor at the trial, argued that the owner and management at the clubs were guilty of Organisationsdelikt – aiding and abetting an organisation involved in criminality. “He knew – in the cases brought to court – that the women working at his club were being exploited by pimps,” says Holzwarth. “And he knew the women were trafficked, or rather, he thought that they might be and [still let them work], and that is sufficient for a conviction.”
"The court agreed. Sentencing Rudloff in late February this year, the judge remarked: “A clean brothel of this size is hard to imagine.” He said he hoped the convictions would serve as a warning to the sex industry.
...
"For prosecutors like Holzwarth, Rudloff’s conviction is a warning to those cashing in on Germany’s insatiable demand for commercial sex. “Rudloff’s case was not an isolated incident,” he says. “In my opinion, cooperation between brothel owners and pimps is risky but profitable for both sides. A win-win situation … but the case has had an impact already. I think brothel owners will be more careful about dealing with pimps.”
Trouble in Paradise: the rise and fall of Germany's 'brothel king'
Jürgen Rudloff’s chain of ‘wellness spas’ sold sex as a health service for men. But his business model was fatally flawed – as his trial for aiding and abetting trafficking revealed
"Until his dramatic fall from grace, Jürgen Rudloff was the self-proclaimed “brothel king” of Germany. Owner of a chain of clubs he boasted was the “the largest marketplace for sex in Europe”, he was every inch the well-dressed entrepreneur, a regular face on reality TV and chat shows.
"Rudloff is now serving a five-year sentence for aiding and abetting trafficking. His trial laid bare the misery and abuse of women working as prostitutes at his club who, according to court documents, were treated like animals and beaten if they didn’t make enough money. His imprisonment has dismantled the idea of Germany’s “clean prostitution” industry and raised troubling questions about what lies behind the legalised, booming sex trade.
"Prostitution – legalised in Germany in 2002 – is worth an annual €15bn (£13.4bn), and more than a million men visit prostitutes every day. The change in the law led to a rise in “super brothels”, attracting tourists from countries where such establishments are illegal.
...
"The Paradise business model is the same as the hundreds of other “sauna clubs” across Germany – brothel owners provide the premises, and the women are self-employed. Yet Rudloff’s high-volume, low-cost model only works if the supply of women is enough to satisfy demand and bring enough customers through the doors.
"According to court documents, this became a problem for Paradise almost immediately. There weren’t enough women to fill the clubs. So Rudloff’s friends in the industry offered to help him out.
"In 2008, as Rudloff was growing his business, investigators in Augsburg, Bavaria – a hundred miles from Stuttgart – received a tip-off that gangs from the city were trafficking women from eastern Europe, and sending them to work in Paradise. (While prostitution is legal in Germany, pimping and sex trafficking are not.)
...
"Peter Holzwarth, the chief prosecutor at the trial, argued that the owner and management at the clubs were guilty of Organisationsdelikt – aiding and abetting an organisation involved in criminality. “He knew – in the cases brought to court – that the women working at his club were being exploited by pimps,” says Holzwarth. “And he knew the women were trafficked, or rather, he thought that they might be and [still let them work], and that is sufficient for a conviction.”
"The court agreed. Sentencing Rudloff in late February this year, the judge remarked: “A clean brothel of this size is hard to imagine.” He said he hoped the convictions would serve as a warning to the sex industry.
...
"For prosecutors like Holzwarth, Rudloff’s conviction is a warning to those cashing in on Germany’s insatiable demand for commercial sex. “Rudloff’s case was not an isolated incident,” he says. “In my opinion, cooperation between brothel owners and pimps is risky but profitable for both sides. A win-win situation … but the case has had an impact already. I think brothel owners will be more careful about dealing with pimps.”