Marketplace apps with live bidding everyone can trust.

Why auctions change the engineering

Because in an auction everyone has to see the same price at the same moment, and exactly one person can win.

A marketplace with bidding looks like a classifieds app with one extra button, but that button changes most of the work. In an ordinary marketplace, a screen that is a second out of date goes unnoticed. In an auction, everyone has to see the same price at the same moment, and exactly one person can win. We design the bidding around that from the first day, with the server deciding every bid, one clock for everyone and updates pushed to every open screen.

What we’ve built

Smart Marketplace is a buy, sell and bid app we built for a client in Flutter, with a Node.js backend. It covers vehicles, properties, electronics, fashion, services and crafts, with real-time auctions and bid notifications, instant messaging between buyers and sellers, search with many filters, listings near you first, secure payments, and seller verification and reputation. It runs on AWS, with Redis caching and images served through a CDN.

Our guide to building a real-time bidding marketplace app explains the decisions behind it in detail.

The marketplace around the bidding

Most of a marketplace app isn’t the auction. It’s the listings, which need different details for a car, a flat or a jacket, the search and filters that help people find them, the photos sellers upload from their phones, and the chat where buyers ask questions before they bid. Each of these has to stay fast as the number of listings and users grows.

Payments and trust

Strangers only trade when they trust the platform. We plan the payment flow with an established gateway, then the less visible parts: matching every payment to its order, refunds, disputes and whether the platform holds the buyer’s money until the item arrives. Seller verification, ratings and a review step for new listings keep the marketplace safe. Rules on auctions and on holding other people’s money differ between countries, so we recommend taking advice for the markets you plan to launch in.

A sensible first release

A first version doesn’t need every feature. Listings, search, one type of auction, payments, chat and notifications are enough to prove that people trade on it. Groups, recommendations and more auction formats can follow once real buyers are bidding.