I`m with the refund folks! While in college, I worked at a shoe store in a mall where the owner would ONLY give store credit. The owner didn`t care if the shoes fell apart in the box on the way home, he would NOT give you anything but credit. It was a dumb policy anyway but in a town where 75% of the residents were transient college students, it was really stupid.
Consequently, he had STACKS of letters from the Better Business Bureau (back in the day before the internet and they were the only way to complain) that he usually tossed in the garbage each month. One day a man who was graduating from the university and moving out of the area came in with a store credit certificate his wife had received and demanded his money back. He created a scene that caused us to call security. Every customer in the small store and half the people walking by saw what happened and probably made a mental note to never go into that shoe store again. The owner was not in that day and when I called him, he refused to come in to handle it and refused to allow me to give the man his money. I quit the next day.
Don`t anger your customers. They will tell their friends.
And, make sure your policy is clearly posted. I would give it a time limit of 30 days, though. And require an original receipt.