In the UK that only applies to unsolicited goods, not to genuine errors. So, if Nintendo were to send you a switch and then ask you to pay for it, sure, you can

In the UK that only applies to unsolicited goods, not to genuine errors. So, if Nintendo were to send you a switch and then ask you to pay for it, sure, you can ignore the demand. If you buy a switch from Nintendo and they send you two you have no right to keep the second (or third, in this case). That said, if the seller makes a mistake then they need to rectify it entirely, they can't demand you wait around for a courier at an inconvenient time or get you to pay for postage.