The concept of a coupon website is similar to an affiliate website, and that is to generate sales for others.  

But these websites leverage a brilliant psychological notion that encourages people to buy, and that is to offer discounts or coupons.
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Statistics show that coupons and discounts are the most prominent influencers of purchase decisions made by internet users.

Discount websites make money through affiliate marketing, when a visitor clicks on buttons like “View Deal,” “Get Deal,” “See Deal,” etc. they’re being referred to a merchant site through an affiliate link. 

Websites earn commissions when their referrals buy products.

This system also works in other way, merchants assign specific coupon code to a particular coupon website, when a buyer clicks on buttons like “Show Code,” “Show Coupon” he is shown the previously assigned coupon code. 

When the buyer enters that coupon code at checkout, the merchant knows from where the buyer had been referred, and the coupon website is rewarded with commission.

Some of the top discount/coupon websites such as Groupon, Retailmenot, Techbargains and more use this model to earn millions of dollars every year.

You can implement the same idea in your niche and make money. 

People are always searching for coupons and discount offers when they’re about to buy something. 

You can dig out such keywords in your niche and rank your website in search engines to generate free traffic and passive income.

You can also promote coupons on social media and try to generate viral traffic as people love to share them with their friends.