Multi-vendor marketplace

Money is the part that has to be right first. One buyer pays once for a basket containing three sellers' goods, and that single payment has to split into three settlements, minus your commission, minus refunds that may arrive weeks later, in a form an accountant can reconcile. Doing this by moving money through your own account turns you into a regulated payment business in most jurisdictions, which is why marketplaces use a provider built for split payments and onboard each seller as a sub-account. Choosing that provider is one of the first decisions, not one of the last.

Then there is the cold-start problem, which is commercial but shapes the software. Buyers arrive for selection and sellers arrive for buyers, and at launch you have neither. Every marketplace resolves this by being narrow first — one category, one city, one kind of seller — and the product should support that rather than fight it. Building a general-purpose platform for a marketplace that will spend its first year in a single vertical is effort spent on a future that may not arrive in the shape you expect.

Catalogue quality is the failure nobody plans for. Sellers upload what they like: the same product under four names, missing dimensions, photographs taken on a kitchen table. Search and filtering are only as good as the data behind them, so the marketplace needs required attributes per category, some normalisation, and a way to merge duplicates — enforced at upload, because cleaning a catalogue after the fact is a permanent job rather than a project.