Sneaking extra items into a user's basket is no better than taking one out. During checkout, users want to see what they're purchasing — no more, no less. Unfortunately, some products and services don't follow this simple rule. For example, apps and websites might offer goods for free, but once users agree, they'll add the item to the basket for a price. 

Sometimes, this dark pattern may have good intentions. For example, Dutch Royal Airlines adds an extra charge to your flight's price to compensate for your carbon footprint.^[1] But while caring about the environment is noble, allowing users to make a conscious decision is much more beneficial. So what can you do instead? 

Provide suggestions and recommendations based on users' shopping history. When users feel the freedom to choose, they're more likely to buy the product or at least consider it. Research shows that positive emotions toward a brand have a significant influence on loyalty.^[2]