The three core roles
- Buyer — searches, purchases, messages sellers, leaves reviews
- Seller — creates listings, manages availability/inventory, receives payments, responds to buyers
- Admin/moderator — reviews listings, handles disputes, manages platform-level settings
Permission boundaries that actually matter
A seller should never see another seller's sales data; a buyer's payment details should be scoped tightly; admin/moderator access to dispute evidence needs its own careful boundary — see How to Plan Roles and Permissions in a Web Application for the general design discipline this follows.
Additional roles as the platform grows
A support-only role (can view but not moderate), or a finance-only role (can see payout data but not listings) — usually added once the platform has grown past what the core three roles can cleanly cover.
Designing this before development starts
Same principle as any web application — retrofitting role boundaries after launch is more expensive than planning for them during the App Scope conversation.
Questions
Do buyers and sellers ever need the same account?+
Some marketplaces allow a single user to be both — this needs explicit design (can they buy and sell simultaneously, and does that create conflicts of interest?).
Who resolves disputes?+
Typically the admin/moderator role, with defined access to the specific evidence (messages, transaction records) needed, not blanket account access.
Can roles be added after launch?+
Yes, but planning the core three properly upfront avoids the most expensive retrofits.