Which supermarket deals can you trust (and which are rubbish)?

We’re all on the lookout for a bargain at the supermarket. When money is tight, it’s important to save where you can. Even when money isn’t an issue, it always feels good to grab a bargain.

But are you always getting one? Research by Which? has shown that shoppers are routinely being ripped off by so-called discounts and offers.

So how do you know what’s a decent deal? And what should you steer well clear of?

Multi-buy money deals – be suspicious

The Which? research showed that one in 10 products in a multi-buy deal, such as a buy-one-get-one-free offer, have their prices raised just before the promotion.

For example, one supermarket sold a pizza for £1 but then increased the price to £2.50 before selling two for £4.50.

Unless you have a photographic memory, it’s impossible to remember all the prices so you won’t necessarily notice.

The good news is that you don’t have to. The online tool mysupermarket.com shows you a graph of each product’s price over the last year.

That means you can see if a price has been artificially hiked to make the offer look better. Not everyone wants to do their shopping online, but you could always use the tool to see how much your shop will cost before you go.

[Related feature: How to beat the latest supermarket tricks]

Product discounts – be suspicious

The same goes for straightforward discounts. I almost never buy a full-price bottle of wine and wonder if anyone really spends £9.99 on a bottle worth a fiver.

Just as with multi-buy deals, there have been accusations of supermarkets inflating the price in order to factor in a discount later.

According to Which?, one supermarket raised the cost of blueberries from £1.80 to £3.99 for two weeks, before putting them on ‘offer’ at £1.99.

Not only that but retailers have been spotted leaving products on offer for longer than they were being sold at a higher price. For example, one supermarket sold Becks beer for 70 days at a higher price before discounting it for 190 days.

It’s hard not to feel misled. Again, checking the prices independently through a tool like mysupermarket.com or by keeping previous receipts can help you spot this.

Bigger bag, better value – be suspicious

It’s easy to assume that the larger quantity we buy of a product, the better the discount. Most of us would expect that a packet of 250 teabags would be cheaper per bag than a smaller packet of 80. And quite often, that is the case.

But reasonably frequently, it’s not. For example, one supermarket sells four cans of Heinz beans for £2, making the unit cost 50p. But it sells a packet containing six cans for £3.19, which is 53p each.

Many of us sleepwalk into paying more by assuming a bigger pack means better value.

Sadly, many supermarkets make it hard for customers to spot these phoney bargains. Few people will know if they are better off buying a packet of three onions for 94p or a handful of loose onions at 87p per kilogram, particularly when they are shopping in a hurry.

Which? has been campaigning for clearer pricing per unit so that customers can make an informed choice. Visit their website to sign the petition.

Fight the overspend temptation

Supermarkets are on a mission to get us through their doors and, once we’re in, get us to spend as much as possible.

And they’re clearly succeeding. We do buy unplanned items when they’re on a two-for-one offer, or sitting in reduced-priced bins at the end of aisles, that’s exactly why supermarkets put them there.

In fact, new research from HelloFresh, a recipe and ingredient delivery service, found that the average Brit overspends by £27.42 every time they visit the supermarket. On a weekly shop, that’s more than £1,400 a year!

But you can fight back. Write a shopping list, based on a meal plan, and then stick to it. Set yourself a strict budget for each shop. Only visit the aisles you need, to avoid aimlessly browsing the shelves.

Most of all, be aware of the temptation to overspend so that you’re only tempted by genuinely good deals.

[Related feature: A fanatic’s guide to supermarket savings]

Which deals are worth it?

Of course, many multi-buys, larger packs and other offers do give shoppers great value. But knowing what to look for can help you find the genuine deals rather than supporting supermarket’s wily marketing.

There are also discounts and offers that you should always take advantage of. If a non-perishable item that you buy regularly is on a particularly good deal then stock up.

If you’re given a discount voucher to spend on your next shop, keep it handy. I have started pinning mine to my bag for life, so I remember to use them next time. This might sound extreme, but it only take a couple of seconds and helps me save pounds off my shopping.

Finally, if you regularly shop at a specific supermarket then make sure you’re making the most of any loyalty scheme it offers.

At Tesco, for example, you can earn one point for every £1 you spend and 100 points is worth £1. So, for every £100 you spend, you earn £1 in vouchers.

However, if you spend your vouchers on the right rewards instead of groceries, they can be worth up to four-times as much. So, for every £100 you spend in store, you can earn £4 in vouchers if you spend them on magazine subscriptions, meals out or other treats through Tesco’s website.

Sainsbury’s customers can make use of the Nectar card reward scheme.

If your regular supermarket offers a reward scheme then it’s well worth signing up – you’re subsiding it either way!