I just had a similar thing happen to me at Border's a couple weeks ago. At Border's, they send you discount coupons all the time, pretty much every week. I took a 40% off coupon and bought an item. For some reason, that I can only attribute to fatigue and hunger, I also bought an item at full price at the same time, even though I knew that I could just wait another week for another coupon. And sure enough, the next day, there was another 40% off coupon in my e-mail. So I called the store and asked if I could return the item (and I asked if I could return it when I bought it and they said yes) and then re-buy it at the 40% off price. And they said I couldn't. Of course, I could do what you're suggesting which is to return the item and come back later and bring the 40% off coupon to get the discount. I also know that Amazon has the same item at 32% off, so I could just return the regularly priced item and buy it at Amazon for 32% off. And I seem to recall that Amazon owns Border's, so I'd just effectively be doing the same thing -- returning the item to the store and buying it from another part of the store.
But alas, I did neither of these things. I just kept the book. It was just a few dollars, and at the end of the day, I couldn't be bothered. And that's how Border's made a few dollars off me and lost some good will. I'm not happy about the outcome, so I wouldn't suggest you doing the same.