Again before anyone jumps in to remind me that they're a business out to make a profit (shock horror) - I know, but these vouchers do seem to be aimed to mislead/ suck people in as opposed to giving their customers a genuine reward.
What does this sound like?
Buy one item with us today - it might only cost you a penny and we'll put £10 credit right back into your account to spend with us...so in effect the item you're buying today is costing you nothing - even when you take the postage and packaging into account.
.....It sounds good doesn't it?
A lot of people are wary, a lot of people have grown wise to this. They've read the t's and c's when they've eventually found them, watched the screen, they've discovered that you can't use them online, then they've tuned in, watched for a couple of hours and realise there's actually NOTHING so far that's eligible for redeeming the voucher, and time's running out! Oh hang on a minute...here's something...mmmm do I need weedkiller, I live in a high rise block of flats?! They've come to realise that collecting the vouchers isn't worth doing either cause they all have to be used within the same timescale and have to be used separately.....Then there's the other people, those who've taken the offer at face value, listened to what the presenters have had to say, bought that extra item 'cause it'd be rude not to!!!! and I'm sure every single day hordes of people fall into the net - Kerching!