Twice in the past week now a cashier has tried to convince me that I should buy more of whatever it is I was buying because it was on sale. Both times I've had to explain that I don't want or need more, and I don't need to pay more for something I don't need or what. I think both times the cashier has been confused as to why I haven't wanted to take advantage of this great deal.
Example 1 - Last week Jeremy and I went to Kohl's to buy him a shirt and tie for my graduation. His only nice dress shirt is black so it's not very practical to wear in the spring and summer. He's actually needed to wear a nice shirt on a couple of occasions recently so we decided it was time for him to get another nice dress shirt. The shirts were buy one get one half off. He only really needed one so we only got one. The teenage cashier boy kept telling us we could get another for half the price and didn't we want to go pick out another one? We kept saying "no" and finally I said "that's $20, we don't want to spend another $20!" We had no reason to spend the extra money for a shirt Jeremy didn't need. He doesn't wear nice shirts enough to justify the extra money. And we're poor grad/post grad students.
Example 2 - Today I went to the gas station down the road to buy some skor bars for a cake I'm making. I took three to the cash register and the lady told me to get another because they were 2 for however much. I told her I only needed 3 but she insisted I should get a fourth because I'd be paying almost the same price for 1 as I would for 2. I told her I didn't need a fourth and I wouldn't eat it so there was no point in getting it. She just kind of said "okay..." like I was an idiot and rang me up. I didn't think it was practical to pay the extra $0.25 or however much it was to get a candy bar I didn't need. If it was fruit or something somewhat nutritious, I would have thought about it. But for a candy bar, no.
I think sales try to trick people. It's like "oh! This is on sale! I must get it!" It doesn't matter if you need it or not. I've started clipping coupons recently and I've been trying really hard to only use the ones that our for products we actually use or for new things that we might want to try. There is no point saving a dollar off of something that we won't eat/use or don't need to eat/use.