Most of the big businesses use pricing strategies to attract customers and boost the sales of their products.
Two of these strategies are mentioned here. Bundle pricing and Buy one get one free.
These strategies are very useful because it plays with the psychology of the consumers. When consumers use a product on regular basis, they want to get it on less price. If some offer like bundle pricing is there, they will purchase the product more than their use at that specific point of time. For example, if a shampoo of 250ml is sold at $5, but in bundle offer 3 bottles of shampoo of 250ml are sold at $10, consumer will purchase the bundle pack. It is actually a win-win situation, because customer is paying less for the product and the company sale has increased from one bottle to 3 bottles.
Similarly, buy one get one free will also trigger the psychological side of the consumer and he will buy the product just because an extra unit is given free, even if the consumer does't need that product at the moment.