Well it's just like booking a courier (as in Royal Mail, DPD or whoever) to collect something from you and deliver it to someone else, only you put them as the collection address and yours as the delivery! You do need to agree with the sender when the pickup will be, obviously, and you need to trust them to pack it up properly - and if they're prepared to do both those things one might wonder why they didn't offer to post it in the first place.