Does 'up to 50% off' pull people into a sale?

Probably, though nobody has actually shown it. The competition regulator's evidence review points to an Office of Fair Trading study that found "strong evidence that price framing", meaning the way a price is presented, "exerts a powerful effect", but nobody has tested the "up to" headline itself. The rules are clearer. A headline that exaggerates the sale can break the advertising code, and consumer law too if it's likely to change what shoppers decide. For a breach of consumer law, the CMA says fines run to "10% of your turnover, or £300,000, whichever is greater".

Our interest, stated first. We run paid ads, sale adverts included, so a big headline figure that pulls people in suits us. That still doesn't make it safe to use one your range can't support.

This is the fourth part of our series on sale prices and urgency, checked. It sets out what the evidence and the regulators say, with a link to each source, and it isn't legal advice.

What the study does and doesn't show

The study dates from 2010, and the review's examples of price framing are bundling, splitting a price into parts, and showing a higher reference price. None of those is an "up to" claim, and we found no independent study of what an "up to" headline does for a small shop.

When an "up to" figure is fair

It depends on how much of your range carries the top saving. The advertising code says price claims such as "up to" and "from" "must not mislead by exaggerating the availability or amount of benefits likely to be obtained by the consumer".

The Chartered Trading Standards Institute's pricing guidance goes further: "You should only make such a claim if the maximum reduction quoted applies to a significant proportion of the range of products that are included in the promotion". It doesn't say what counts as a significant proportion, but one half-price item in a large range is unlikely to be enough.

Small print won't rescue a headline either. In an example from the CMA's guidance, an advert says televisions are heavily discounted and a tiny footnote says only a few of them are. If shoppers wouldn't notice that footnote, and would have decided differently had they read it, "they will have been deceived by the overall presentation and misled".

Setting a headline your range can support

• Count how many lines actually carry the top discount before you set the headline.
• If only a few items carry the top saving, use a lower "up to" figure, or show the smallest saving alongside the largest.
• Put any conditions, such as a minimum spend, next to the figure rather than in a footnote.
• Every saving still needs a genuine usual price behind it, and that's the subject of our piece on using a 'was' price in a sale.

What to discount, and by how much, is a decision for your digital marketing strategy rather than for the advert. Once the advert is running, the paid side raises its own questions, from how much Google Ads cost to why Google Ads aren't converting.