"At this time of the year, what you have got is the students going home for the summer so they actually give up their accommodation and then come back in February for the start of the new year.
Consequently, that adds to your over-supply and so to get rid of the properties, people give one to two weeks of free rent or reduce the overall rental.
"Another issue as well that has a fluctuation and bearing on rental prices is that the houses [in Wanganui] tend to be older houses without insulation and without quality heating and people have become very transient in looking for houses that do have these things," she said.
"It has become really important that we try to educate our investors and our landlords to do what they can."
Ms Ellis said the decline created the perfect conditions for tenants but landlords had cause to be concerned.
"People wanting to rent have more choice on where they want to rent and providing they are good tenants then they can get into a half decent home.
"Landlords however are a little worried at the moment, particularly with the Government's latest announcement about looking at the rental market at how many properties you own and trying to find out whether or not [the Government] can get more tax out of you."
The company expected a quiet Christmas followed by a busy new year, she said.
The Trade Me data showed the November median rental price for a small house (1-2 bedrooms) in Wanganui was $170 while it was $220 for a medium house (3-4 bedrooms). The median rent price for a large house (5 plus bedrooms) was $270 - a 30 per cent decrease compared with November 2013.
Nationally, rental prices increased by 5.3 per cent last month, compared with November 2013.
The median rent price was $400 per week in November, where it has hovered for the past several months.
The national median rental price for a small house (1-2 bedrooms) was $320, up 8.5 per cent from the same time last year while it was $450 for a medium sized home (3-4 bedrooms), also up 9.8 per cent. Large houses (5-plus bedrooms) increased by 8.3 per cent to $650.
Head of Trade Me Property Nigel Jeffries said the median weekly rent had been "stuck in the mud" for four consecutive months.
"There's less price pressure on tenants and a healthy supply of properties for rent in many areas. Although the weekly rent is holding steady at $400 per week, the year-on-year increases are trending down."
In the past five years, rent prices countrywide have increased by 21.2 per cent.
The data showed Auckland was the most expensive place to rent a home in November with an average asking price at $460 followed by Christchurch at $450 per week.
