Multi-vendor commerce is an operations problem.
The storefront is the easy part. Seller boundaries, catalogue ownership, order splitting and fulfilment are where the architecture becomes real.
One checkout can create many operational realities
A customer sees one basket. The platform may see multiple sellers, different stock ownership, different fulfilment rules, separate payment or settlement concerns and different exception paths.
Seller flexibility creates platform responsibility
The more autonomy vendors have, the more disciplined the platform has to be about permissions, product ownership, order state and auditability.
Do not hide complexity—contain it
Good marketplace architecture does not pretend the business is simple. It contains complexity behind clear domain boundaries so customers and operators do not have to carry it manually.