The chicken-and-egg problem
Buyers won't come without sellers; sellers won't come without buyers. This is a business/marketing risk, not a technical one — no amount of good engineering solves it on its own, and it's worth having a real plan for seeding one side before launch, not just after.
Payment and dispute complexity underestimated
Disputes (buyer says item wasn't as described, seller says buyer didn't pay) need a defined resolution process — building this reactively after the first real dispute is a common, avoidable mistake. See Marketplace Development for how payment/dispute logic is scoped upfront.
Moderation load underestimated at launch
Manual moderation (the right MVP choice — see What Features Should a Marketplace MVP Include?) takes real, ongoing staff time that's easy to underestimate before you've seen real listing volume.
Building the full platform before validating demand
The single most common, avoidable risk — see Marketplace MVP vs Full Marketplace Platform for why starting narrow specifically protects against this.
Questions
Is the chicken-and-egg problem solvable with better technology?+
No — it's fundamentally a demand-generation and business-strategy problem, not something engineering alone solves.
How much moderation staff time should we budget?+
More than intuition suggests before you've seen real listing volume — worth tracking closely in the first weeks post-launch.
What's the single biggest avoidable mistake?+
Building full-platform automation before validating that both sides of the marketplace will actually show up.