Confidence is key. A few years ago, coupon generators where all the rage on 4chan. A friend of mine that's a huge /b/tard ended up printing himself up a few solid ones right after the release of the slim 360s. He called up a friend for a ride, drove to a Walmart out of town, picked up a 360 slim and started checking out. When it was time to pay, he gave the cashier his fake coupon, who scanned it and said it was giving her an error. He ask if she could get the manager. When the manager got their he explained to him that he had received this coupon from Microsoft after his old 360 RRoD'd. He told him he had to talk to customer support for a few hours before they finally gave him it. The manager, who happened to be a huge gamer, started sympathizing with him. While the manager manually took the price off since the coupon wasn't scanning, they chatted about Microsoft's sucky customer support and some of the horror stories they'd heard people had to deal with. When the transaction was complete, he thanked the manager and walked out. A free $300 slim xbox for simply having a piece of printer paper and balls. But he wasn't done yet. He felt bad that he bummed a ride from his friend and made him drive a few towns over, so he decided to get him one too. He just went to another Walmart, pulled the same ploy, and walked out with a second free 360. After all this, he got on 4chan and posted the pictures of his receipts. It was hilarious seeing the receipt say,
"$300.00
-$300.00
Total: $0.00"
All that being said, stores started cracking down on stuff like that right after, because it is illegal to do.
But like I said,
confidence is key.