The biggest shopping rip-offs

How do we identify the biggest shopping rip-offs?

Consumer group Which? has been busily putting its nose where it belongs. In an investigation into environmentally-friendly products, it found close to half of them lacked evidence to support the green claims in their labelling, or that some claims were exaggerated.

Some of these products were Tesco Naturally toilet cleaner (the packaging of which Tesco has now agreed to alter), as well as toilet cleaners from Sainsbury's, Green Force and Ecover. Which? found no evidence that these were better for the environment than standard toilet cleaners.

Another product that Which? has criticised is Marks and Spencer's anti-cellulite knickers. Whilst it didn't actually test a group of ladies in underwear under laboratory conditions (nice work if you can get it) it did consult three specialists who were highly doubtful that it could work. Marks and Spencer vigorously defended the product.

Which? isn't the only body to investigate on our behalf. EU experts have been putting probiotic yoghurt under the microscope. According to the BBC, they conducted tests on nearly 200 yoghurt health claims and rejected them all as either wrong or lacking evidence. Big players such as Danone and Yakult are working on new or more tightly-worded claims, as well as searching for more evidence.

Getting to the truth

There are usually two sides to the story, and sometimes we just can't know for certain whether something is legitimate or whether it's shopping's greatest rip-off. However, we can make more informed buying decisions if we do a small amount of research, and that should help us to avoid wasting money on the worst-offending products, whether it's food, domestic products, healthcare or health books.

Whether you're questioning the validity of detox diets, homeopathy or anti-wrinkle cream, the internet frequently yields convincing answers if you know where to look.

• Watch this video: The biggest financial ripoffs

Food agencies

A good place to start looking for food-related information is the UK's Food Standards Agency, which collates and assesses research. Its counterparts in the US, the Food and Drug Administration, and in Europe, the European Food Safety Authority, do the same.

All three publish their findings and opinions on the internet. It can take a little searching on their websites to find the relevant information, but I find I can usually get to the crux of their opinions on a product type within 20 minutes.

Scientific journals

Those agencies often link to the scientific articles or journals upon which they based their decisions. So you could simply click through, but, whatever the subject, you could also look up the journals directly. You might use the Journal of Nutrition or Health Affairs, for example. There's a list of other science journals here.

The respectable ones require that all studies are peer reviewed, which means that at least two scientists independently assess them.

Scientific magazines

Unfortunately, however, scientific journals are not easy to search and are probably unintelligible to most of us, as they're written for the science community. Hence, you might find it easier to search science magazines, such as BBC Health and New Scientist. It might mean your research isn't as thorough, but for most of us it's more realistic – and a lot better than relying solely on the word of someone trying to sell us something.

Other sources

If you're still not satisfied, you have other resources, such as NHS Direct. Although there's a huge amount we still don't understand about our bodies and medicine, this site will be able to give you the latest official opinion from the NHS, which may help you to decide whether a particular non-NHS treatment is worth paying for.

The charity Sense About Science teaches us about some of the worst and often very costly science myths.

You could also see if Which? has done any studies into the subject. Whilst it costs money to access most of its website, you can see some of its information in its campaigns section for free.

Which? is pretty good at pointing out misleading labelling. For example, it writes that the packaging for Dairylea Dunkers boasted of a high-calcium content, which is good – but the high saturated fat content isn't.

Which?'s research often gets mentioned in the press so, if you can't find what you're looking for in its campaigns section, try googling for articles that mention Which? along with any relevant keywords for your search.

We can only do the best we can

None of this is perfect. Sometimes researchers, agencies, publications and charities will have their own agendas, will make mistakes, or conduct poor-quality research, even when research comes from peer review.

Our best defence against this is to look for several reports that seem of good scientific quality that all have similar results. That is particularly convincing when the case for the other side is weak, obviously biased, deliberately obscure, or not scientifically presented.

The alternative is just to believe everything we read in the papers, on product packaging or in the blurb of the latest fad-diet book. But that's likely to lead to more poor decisions and to buying more of shopping's greatest rip-offs.

Our worst enemies

Our own worst enemies aren't lazy reviewers, corporate marketing departments, gullible government agencies or industry-funded charities. Our own worst enemy, when it comes to shopping, is ourselves.

Not only do we take what we see at face value, but we test products using our own perceptions or those of our friends. However, our perceptions are frequently deeply flawed. The list of psychological errors we make is a long one, including: subjective validation, confirmation bias, the bandwagon effect, selective perception, wishful thinking, status quo bias and post-purchase rationalisation.

I'm sure many of us can immediately identify with that last one, but the others are extremely prevalent in human behaviour, too. The potential for self-delusion cannot be underestimated.

Many of these also cause the placebo effect, which can be a good thing, but it’s also sometimes very dangerous. It'll often be better and cheaper to spend 20-60 minutes doing some good old-fashioned research.

More: Stupid things people believe about money | A new way to save money on the internet