Tell them before
Not in terms nobody opens.
Fail to tell a buyer about the cancellation right, and the fourteen days become twelve months.
A distance purchase is legally different from a shop purchase for an obvious reason: the buyer never handled the thing. The law compensates for that with a right to cancel within fourteen days of the goods arriving, exercisable without giving any reason and without needing anything to be wrong with the item. It is a statutory right rather than a returns policy, which matters because a policy can be written narrowly and a statutory right cannot be cut down by terms. The clock runs from delivery rather than from the order, so a slow dispatch does not consume it.
The enforcement mechanism is where it becomes interesting, and it is the part sellers tend not to volunteer. Prescribed information must be given before the consumer is bound, including the existence of the cancellation right, its conditions, its time limit, the procedure for exercising it and the cancellation form. Where a trader fails to provide the information about the right to cancel as required, the cancellation period is extended by up to twelve months. That is a remarkable sanction for an omission: a single missing sentence converts a fourteen-day exposure into a year-long one, and it applies to every order placed during the period the information was wrong.
The rest follows the same logic of putting things before the purchase rather than after the complaint. A refund is due within fourteen days of the goods being returned or of evidence that they were sent, and it has to include the cheapest standard outbound delivery the buyer paid, which many sellers quietly omit. The cost of returning goods falls on the buyer only where the trader said so before the contract was concluded, so silence on that point puts the cost back on the seller. Exceptions for personalised goods and for sealed items unsealed on hygiene grounds are real but narrow, and they belong on the item page before a purchase, never in a reply to a cancellation request. And where no delivery period is agreed, thirty days is the outer limit, with risk in the goods staying with the seller until they are physically in the buyer's hands.
Not in terms nobody opens.
At the standard rate.
Never after a request.
Ask first. It costs nothing.