1. They are offering a rebate or sale price as a favor: No, really, people actually believe this. "We're celebrating our 10th anniversary, and as our gift to you, everything is on sale!" People actually think that companies are kind-hearted and want to see you get ahead, so they are holding a sale as a thank-you to consumers!
2. They are offering a rebate or sale price to get you to try a product: No, not really. When a product doesn't sell well, they cut the price. You lower the price, product moves. They are not interested in trying to "win you over" to a shampoo or detergent brand. They just know that your price point is below their nominal price, and that they can move product if they offer it to you at your price point.
3. They are offering a rebate or sale price to move out product at the end of the model year to "make way for the new models!": No, again. A popular product sells out, and there is no "leftover" at the end of the year, unless the leftovers are the undesirable versions (the brown car with green interior).
4. At certain times of the year, such as President's day, they lower prices because, well, prices are just lower then, that's all! The day after President's day, the cost of a car increases mysteriously. So you'd better sign the papers on that deal today or lose out forever! If you can't see this transparent attempt to pressure you, forgetaboutit!
5. The sale price is really a lower price that what others ordinarily pay: The car makers have really shot themselves in the foot with this one. No one pays "sticker" price on a car anymore. And while some car makers are more realistic about sticker prices, they still are just placeholders and not actual prices. When someone offers you "$10,000 off!" a new pickup truck, you have to come to the conclusion that the sticker price is a sad joke. No, the "sales price" is no great bargain, just closer to what you should expect to pay for the commodity.