Groupon customer Sarah Luty, a 31-year-old from Luton, said she had become much more selective on which deals to buy after finding it difficult to redeem one voucher.
As part of Sony's collaboration with Pottermore and the Pottermore Shop (the exclusive home of the Harry Potter eBooks), Sony will offer a voucher to redeem against the first eBook in the Harry Potter series, Harry Potter and the Sorcerer's Stone, for free.