I think some people misunderstand the terminology when signing up for promotions associated with the QCard. The promotional credit applied is a QVC account credit, not a QCard statement credit, which means it is money to spend on a future purchase, not money used toward paying a previous bill. If you read or listen to the formal QVC promotions, you will always see or hear the words "account credit."
However, I've noticed that some hosts have erroneously described it as a "statement credit" even when the text on the screen next to them clearly says "account credit." QVC management should fully train the on-air talent in that respect, as it makes a difference in customer expectations and satisfaction.
As long as you read the fine print (just type Q CARD into the search field on the site), it is very clear what you are getting and the associated timeframes. When I signed up for my Q Card, I had no problem following the steps to get my account credit, so the promotions are definitely not scams.