Melaleuca alternifooledya

Here’s a little test of your observation skills: how much would you expect to pay for one of the bottles of tea-tree oil pictured?

If you said £3.09, you’re wrong. If you said £4.09, I can see that you’ve worked out this is a trick question, but you’re also wrong.

Don’t worry, I got it wrong too. I bought one of the bottles of tea-tree oil from that shelf and I didn’t realise until I left the shop that I’d been charged £7.79 for it.

Why? Well, the advertised price is for a 10ml bottle of tea-tree oil, and the bottles in the picture are in fact 20ml. The sign does say 10ml, so Holland & Barrett (for it is they) could argue that there’s nothing to complain about. If I don’t read the whole sign properly before grabbbing a bottle of tea-tree oil and heading to the checkout, that’s my mistake, right?

Well... no. I don’t think it’s that simple. For several reasons.

1. The 20ml bottles are the only containers of tea-tree oil visible above the sign advertising the £3.09 price. (Presumably the 10ml containers sold out.)
2. The real price of the 20ml containers is almost completely obscured by a sign advertising another “£1 off” deal, this time for the 10ml containers of eucalyptus oil. To see the price of the 20ml container I bought, I would have had to physically pull one of the signs advertising the deal off the shelf in order to see behind it. But it wouldn’t have occurred to me to do that unless I’d already noticed that the price given in big letters under the item I was buying was not the price of the item.
3. The print saying “10ml” is significantly smaller than the rest of the print on the sign.
4. The print on the boxes giving their sizes is even tinier.

Just in case it still wasn't an easy enough mistake to make, we've been trained by 2-for-1 offers and bulk-buy deals to accept that generally, the more you spend, the more you save. So it’s counterintuitive that a 10ml bottle of tea-tree oil would cost 30.9p/ml while a bottle twice the size costs 38.95p/ml.

Yes, this is a usability issue. But it’s also a transparency issue. I bought an item I wouldn’t otherwise have bought, because of an advertised offer. I thought I was taking advantage of that offer, but in reality it would have been impossible for me to do so because all the relevant items were sold out. Yes, it happened because of confusing signage and poor stock control, but the fact remains: I was tricked. Does it make any difference that I was tricked by poor usability rather than by a smooth-talking salesman?

There’s a saying which people sometimes quote at me: “Never ascribe to malice that which can be explained by incompetence.” I think it’s a very stupid saying, and maybe one day I’ll write a whole blog post explaining why. But right now, I’ll just say: poor usability allows businesses to mislead their customers and pretend it’s incompetence rather than calculated dishonesty. It also causes businesses to mislead their customers without any intention to do so. The result for the customer is the same. That’s one of the many reasons why I think usability is so important.