The ad may look appealing, but all is not what it seems.

As New Zealand house prices and rents continue to skyrocket, those in financially vulnerable situations are turning to prostitution.

New Zealand Union of Students' Associations national president Rory McCourt said many students facing financial hardship turned to sex work in order to cover living costs.

International students were at the greatest risk, McCourt said.

And with rents in New Zealand up $25 a week over the year to April advertisements offering "free rent for services" are springing up across mainstream house-sharing sites.

An ad posted on Craigslist in Auckland offers a free bedroom in the suburb of Glen Eden in exchange for "sexual favours."

An advertisement for a room in Auckland in exchange for sexual favours that was posted on Craigslist.

McCourt said he had not heard that students, who were unable to afford accommodation, were living rent free in exchange for sex.

However, it was not uncommon for students to enter the sex industry to cover mounting living costs and a lack of student allowance and loan increases.

This arrangement worked out well for some students, but not for everyone, he said.

BEEN HAPPENING HERE 'SINCE TIME BEGAN'

Further accommodation support from the government was needed for tertiary students, especially those in the main centres, McCourt said.

Increases in student allowances and living costs introduced in April were not enough to cover student rents, which put students in financially vulnerable situations.

Some financially vulnerable students were forced to buy less food and sacrifice their health in order to pay rising rent costs, he said.

New Zealand Prostitutes' Collective (NZPC) national coordinator Catherine Healy said sex in exchange for accommodation could be considered prostitution, but that it was not a new phenomenon.

It came down to whether the person providing the sexual services felt they were engaging commercial sexual activities, Healy said.

It was a grey area, which became less clear the longer the people lived together, she said.

Once the people had been living together for a while it could be considered to be a de facto relationship rather than a commercial one, she said.

Healy said while she had not heard of sex for rent arrangements in New Zealand, she had no doubt this did occur.

"I'm sure people have been hooking up together since time began for mutual needs."

If the person did feel they were engaging in commercial sexual activity and their rights had been breached they would be covered under the Prostitution Reform Act, she said.

Healy said she knew of many students, including international students, who turned to sex work in order to finance their way through university.

LISTINGS ON TRADE ME

Trade Me spokesman Jeff Hunkin said listings of accommodation for sex were not common on the online auction site.

There had been an "extremely small handful" of similar listings that had been removed in the past on the grounds of "bad taste", Hunkin said.

Trade Me did not have a specific policy in relation to accommodation in exchange for services, including sex, but when listings overstepped the mark they were removed by a policing team that monitored the site 24/7.

The public was good at alerting Trade Me to any listings that crossed the line or were in breach of the sites terms and conditions, he said.

"We'd also encourage anyone renting accommodation to familiarise themselves with their rights under the Residential Tenancies Act, in particular when it comes to lodging bond and arranging rent."

ALSO HAPPENING IN OZ

The same thing is happening across the ditch as Sydney house prices creep towards a median of AU$1 million (NZ$1.07 million).

One advertisement for Sydney accommodation on Craigslist read: "Are you a lovely female needing a room for a night or two . . don't want to pay over the top hotel fees?"

The advertisement continued, "My place is clean, close to transport and CBD ... the only catch is there is one bed only."

"A friends with benefits arrangement?"

Another advertisement is more detailed: "You've probably figured out the arrangement already, so let's get down to specifics."

"ME: Handsome, tall, in great shape, generous, self-employed, late 30's,"

"YOU: Young (under 21), gorgeous, adventurous, looking for free rent ... "

CAN BE MISINTERPRETED

In several Australian ads, subtext can be lost on the vulnerable, particularly those with limited English.

*Tom has "a free room available in kings cross area for the right Guest...Obviously looking to make an arrangement. But flexible in what that is".

Alison Ye, 26, is an international student from China, who was shocked by Sydney's high rent.

"The equivalent in Beijing was around $150 a week, and here is so difficult," she said.

Two days after placing an advertisement on Gumtree for "cheap or free rent in exchange for cleaning and cooking", a young couple asked Ms Ye to share her body instead.

"It was so creepy and kind of scary because it was in person, and there have been lots of emails from older single men, which I find weird.

"I am scared sometimes I will agree to something I don't fully understand in English," she said.

Professor Bill Randolph, of the Australian Housing and Urban Research Institute, says the phenomenon is driven by housing cost, combined with a culture of anonymity.

"Years ago, you couldn't have this kind of access to people and be hidden.

"Now, this is the opportunity for people to exploit the vulnerable, who desperately need housing they can afford," Professor Randolph said.

Terry Bincett has offered space in his queen-sized bed in Matraville for $22 a day, through a Craigslist advertisement for those who "aren't shy". He likens the offer to meeting in a bar and taking them home, but says sex isn't a necessary part of the deal. "It is whatever people are comfortable with, and they can choose to have their own room," Mr Bincett said. In one year, he has attracted eight guests; two women and six men, all but one of whom have been unperturbed by the intimate sleeping arrangements.

"One guy in the US spoke to me at 12.30pm on a Wednesday, and was at my door by 6am that Friday!" he said.

As a co-founder of independent share site Flatmatesfinders.com, Guy Mitchell has made it a policy not to publish posts that allude to exchanging sexual services.

"We read and monitor all submissions and watch for this kind of thing.

"We want our site to be a reliable and safe place for people to find housing," Mr Mitchell said.

OR ... BIBLE STUDY

A more wholesome alternative could be this offer by an unnamed Gumtree poster in Ramsgate, seeking Christians only.

The way tenants make rent is to "cook and clean a little", but Bible study is compulsory.

The landlord, who wishes to remain anonymous, said he had a number of people move in and "profess to be Christians, who have found excuses to not join in Bible studies".

"It's only an hour and a half a fortnight, it's not asking a lot," he said.

The site LoveRoom offers a similar arrangement but with a dating twist.

LoveRoom is similar to Couchsurfing but users connect with people they are attracted to and stay at their house for free. LoveRoom launched in November 2014 and at the time claimed to have more than 10,000 members in 90 countries, including about 800 Kiwis.

- Have you seen ads like this here in NZ? If so, let us know at newstips@stuff.co.nz.

- Sydney Morning Herald & Stuff.co.nz