How to use inventory notifications to grow a marketplace

Two-sided marketplaces often grapple with the chicken-or-the-egg problem, where attracting both buyers and sellers simultaneously poses a challenge. Successful marketplaces like eBay, Zillow, Lyft, and Discogs have overcome this by implementing engaging inventory notifications that keep buyers interested and returning. Features like eBay's watch list, Zillow's saved homes, Lyft's price lock, and Discogs' Wantlist help maintain user engagement by notifying buyers about inventory changes or opportunities, thereby encouraging both buyer and seller participation. These notifications work particularly well in contexts of scarcity or urgency, such as with limited-time offers or unique items, driving user action and improving conversion rates. However, engineering these notifications requires a robust system to efficiently manage and deliver alerts without overwhelming users or systems. Knock offers a solution to the complex engineering challenges by providing a streamlined subscription model that handles the logistics of notifying large numbers of users, allowing marketplaces to focus on enhancing user experience without the technical burden.