Actually you're both wrong. BIGI sale with a BIGI coupon only results in 2 free items. You purchase 2 items - the store gives you one for free as part of their deal. Your coupon gives you the second item for free. The coupon still attaches the one the store gave you for free as the one you 'bought'. This is perfectly legal, as the coupon represents payment for an item. Some stores probably won't allow it, but Target, Walmart, CVS, and Walgreen's all do. The store will be reimbursed in full for one of those items.
I get frustrated when people assume that couponers are 'scamming' the stores or manufacturers just because they take advantage of store sales when using the coupons. I also get frustrated knowing that there ARE people out there who are abusing the coupons by making photocopies or trying to use them in the wrong way. I find that the majority of store employees are not aware of their own coupon policy, and I have had to explain it to them many times (print-out in hand) so they understand what they're supposed to do. But I NEVER use coupons in a way that I'm not supposed to, nor do any of the women in the 'coupon community' that I communicate with online. We frown upon it.