Ten years ago, buying clothes online felt like a gamble. If a shirt did not fit, you were often stuck with it, or you paid to post it back. Today, many online shops offer free returns, and shoppers have adjusted. It is now common to order the same jacket in three sizes, keep the one that fits and send the other two back. Shopping has never been easier. But a service that costs the customer nothing still costs someone something.

Consider what happens to a returned parcel. It has to be collected, carried back to a warehouse, opened, checked for damage, cleaned if necessary, repacked and recorded before it can be sold again. Each step takes time and labour. For an expensive coat, the effort is worthwhile. For a cheap T-shirt, it can cost more than the shirt itself is worth. In those cases, retailers may sell returned goods in bulk to discount companies at a fraction of their price, and some simply throw them away.

The environmental cost is harder to see. Extra journeys by delivery vans add to traffic and pollution, but one transport researcher points out that a van carrying a hundred parcels does not make many extra trips just because a few of them are returns. In her view, the larger waste lies elsewhere: in goods that are made, packed and shipped but never reach a customer who keeps them.

Some retailers have begun to respond by charging a small fee for returns. Early reports suggest that customers send back fewer items when they have to pay. Critics, however, argue that a fee hits hardest those who have little choice but to shop online, such as people who live far from shops or who find it difficult to visit them, and who therefore cannot try clothes on before buying.

Other companies are trying to reduce returns without charging for them. They publish detailed measurements, invite customers to say whether an item fits as expected, and offer online tools that suggest a size based on previous purchases. The aim is to make "bracketing", the habit of ordering several sizes of the same item with the plan of returning most of them, less necessary.

None of these approaches is perfect, and it would be a mistake to blame shoppers for using a service that shops chose to offer. The real problem is that the cost of a return is invisible to the person who decides whether to make one. Even if a shop continues to pay for returns, it could show customers at the checkout roughly what each return costs. People who know what something costs tend to use it more carefully. Free returns, in other words, are not free; the question is only who pays, and whether anyone can see the bill.