Steve why do you have them delivered on a signed for delivery service? I am sure the large majority of people who order these will be out at work when the postman comes, so like me will in all probability not be in to sign for them, meaning a trip to the sorting office the next day 
anytime i sell something on ebay etc i always send by recorded delivery to be signed for, mainly for my own benefit of knowing its been delivered, more and more people these days try and scam ya insisting they`ve not received goods and want there money back so for me its peace of mind really
tony