I started couponing last year and had a ton of stuff stocked up by the time our yard sale came around this year. I put stuff out at typically 75% off regular retail prices and sold almost everything!
I do buy things that I don't need, but if a store is going to PAY me to take an item, you better believe I'm going to purchase it. However, I have never cleared a shelf (unless it was the last one or two of something). I also never do more than one transaction per day at the same store.
I have quite a few bottles of Dulcolax (as many of you probably do as well). Last time, CVS paid me $3 to take it. I will then use that $3 to buy something I DO need, like milk.
I also made over $300 selling my stockpile at a yard sale. And, I'll do it again next year. With that being said, I wouldn't buy it at a yard sale for myself (but I don't have to, I have a ton of it at home).