Pop-up ads and upsells are common marketing tools used by online businesses to increase engagement and sales. Pop-up ads typically appear suddenly while browsing, aiming to grab attention with offers like discounts, newsletter sign-ups, or special deals. While many users find them annoying, studies show they can be effective when timed well and designed thoughtfully. Upsells, on the other hand, appear during or after a purchase process, encouraging customers to upgrade their order or add related products. When done right, upsells enhance the shopping experience and increase average order value. However, overusing either tactic can frustrate users and harm brand trust. The key to success lies in subtlety, relevance, and timing—offering value without interrupting or overwhelming the customer experience.