Coupon
Problem summary
You want to attract your users to conduct a purchase of one of your products
Example
Usage
- Use when you want to create special attention around a specific product or service
- Use when you want to give your customers an incentive to commit to a purchase of one of your products or services
- Use when you want to advertise a discount to a specific group of people or advertise to a target group of users by for instance posting a coupon code in a forum or printing a coupon code in a magazine.
Solution
Create a field specifically for entering a coupong / promotional code. Entering a code gives the customer a certain amount of discount depending on what code has been entered. On the merchants side, a number of different codes can be constructed in order to 1) measure where your customers come from and have heard of you and 2) allow different discount rates for different groups.
Rationale
Using coupons codes to attract customers to buy a merchants product builds on the customer’s assumption that the offer is short lived, why action must be taken soon in order not to loose the psychological gain given by receiving the coupon code. As losses are mentally valued with greater weight than gains, the customer will be aversive towards losing the gain given and act on it while time is. Check out the Value Function as proposed by Tversky and Kahneman, 1991: Loss Aversion in Riskless Choice.
More examples images of the Coupon pattern

You can fill out a coupon code when buying at amazon.com

Coupon codes should be entered on a separate process for certain users who may have one, and not appear on the same checkout page as “everybody else.” This can prevent a sale as the user wonders “Where are the coupons and how do I get one?”
I think one of the most obvious reasons for coupon codes is missed here, that is that coupon codes help marketers track the effectiveness of their advertising dollars.