New Zealand has some of the highest grocery prices in the OECD – but being aware of supermarkets' marketing tricks could help you save money.

Bodo Lang, head of the marketing department at the University of Auckland, said New Zealand's supermarket prices stood out internationally.

"There are two key reasons for this: the long distance from major markets which results in increased transportation costs and, perhaps more importantly, the small size of the domestic market which means that we do not have much competition in the grocery retail sector.

"Effectively grocery retailing is a duopoly. The two competitors are Foodstuffs and Progressive Enterprises who each run multiple brands of supermarket but effectively it is two companies that hold the vast majority of the market share."

READ MORE: Duncan Garner: Aisle be damned: Kiwi supermarkets are milking it

His colleague, economist Tim Hazledine, agreed a lack of competition was a key driver of prices. But he said tax also played a part. New Zealand applies GST to food while most other countries do not.

Food prices rose at an annual rate of 0.1 per cent in February. But some types of food are increasing at a faster rate than others.

Statistics NZ figures show that the price of a kilogram of sausages rose 73.7 per cent from mid-2006 to mid-2017.

Beef mince became 58.3 per cent more expensive. Bananas were 56 per cent dearer. Mushrooms were up in price by more than a third. Those price increases do not allow for inflation, so the increases are more in real terms.

How can you reduce your bill? Lang said there were a number of tricks to watch for.

123RF Supermarkets want you to buy your veges first, so you'll feel better about buying biscuits later.

Choose the smaller trolley

He said the size of supermarket trolleys had an impact on how much people bought.

"Bigger carts mean that we tend to buy more. This phenomenon is very similar to dieting research that has found that using smaller plates is one of the easiest ways to reduce portion size and thus lose weight."

Many supermarkets offer a bigger and a smaller option - take the smaller if you can.

Stick to your list

Lang said supermarkets put fruit and vegetables by the door so that customers would pick that up first and feel virtuous. That would then give them "moral permission" to buy more of the less healthy food they encountered later on.

"Another way in which supermarkets can shape what we buy is which categories items are close to. For example, co-locating items based on usage occasions, say beer and chips, can have a big impact on how we spend on such items.

"Similarly, placing highly profitable items close to items that are bought frequently can also have an impact on how much consumers will spend. An example of this would be having alcohol next to bakery items, produce or the dairy section."

Most supermarkets put the things that people "pop in for" - like milk, or a loaf of bread, as far from the door as possible. This maximises the chance that you'll pick something else up on your way through.

123RF Bigger trolleys encourage customers to spend more.

Look down for better prices

Lang said the most coveted position on supermarket shelves was between hip height and eye height. "This is where brands are placed that are selling well and making the supermarket (and the manufacturer) good profit margins."

You may find a similar item at a cheaper price on a lower shelf. Products aimed at kids are often placed at their eye level.

Don't fall for bright signs or big claims

Lang said research had shown that just having a red border on a price sign would increase the number of sales.

"One of the most powerful sales techniques are end of aisle displays. These are typically bought by manufacturers for a certain time period. End of aisle displays work so well because they are visible from multiple vantage points and offer the opportunity to display the product three-dimensionally.

"Consumers can behave like sheep – if others are buying it then so should I! Therefore, another popular technique to increase sales of a particular product is to indicate that it is in high demand. Supermarkets often do this by indicating that customers can only buy a limited amount of a product. This will immediately increase sales because that item has become more desirable."

A spokeswoman for Foodstuffs said there was "significant choice" for New Zealand shoppers, including brands such as Farro Fresh, My Food Bag and Mad Butcher.

"Consumers have a range of grocery options open to them and the ability to shop around to ensure they get the best possible deal. We also encourage customers to look out for promotions and buy produce that's in season to ensure they get the best possible deal."

Countdown did not want to comment.