Building a marketplace sounds straightforward until you're knee-deep in edge cases nobody warned you about. After watching countless marketplace projects stumble over the same hidden obstacles, I've compiled this list of critical issues that are being overlooked consistently.
The "Just show what's available" inventory mess
Your product team says: "Just show available inventory in real-time." But in reality, a seller lists their handmade jewelry on your platform, Etsy, Instagram, and their own website. By the time your customer clicks "buy," it's already sold elsewhere. Now you're processing refunds and apologizing while your trust score plummets.
Most teams discover this after launch when angry customers start leaving reviews about "fake inventory." The real problem? You can't control what happens outside your platform.
Building "real-time" inventory when sellers manage stock across multiple channels is basically impossible. Accept that inventory will be wrong sometimes and build your entire purchase flow around graceful failures.
The payment split nightmare
"We'll just take our 20% commission automatically."
Sounds simple until:
- A customer wants a partial refund
- The seller ships half the order
- You need to refund your commission but already paid the seller
- The payment fails after the seller shipped
- A chargeback comes in three months later
Suddenly your database has negative balances, your accounting is broken, and nobody knows who owes whom. Every edge case creates new states in your payment system that nobody anticipated. Teams often rebuild their payment logic three times before getting it right.
The Search That Gets Worse With Scale
Week 1: "Our search is so fast!"
Month 6: "Why does search take 8 seconds?"
Your beautiful search worked great with 100 products. Now you have 100,000, each with dozens of attributes, seller-specific pricing, location-based availability, and custom shipping rules. That simple SQL query is now a 15-table join that makes your database cry.
The worst part is you can't just "add Elasticsearch" anymore. Your entire frontend assumes instant search results. Your filters are built into the URL structure. Your SEO depends on those search pages. Retrofitting proper search infrastructure means rebuilding half your platform.
The Review System That Backfires
Every marketplace needs reviews, but reality isn't always that simple.
- Sellers create fake accounts to review themselves
- Competitors leave fake negative reviews
- Buyers threaten bad reviews to extort refunds
- Good sellers get one bad review and their sales die
- Bad sellers know how to game the system perfectly
Your team will spend more time fighting review fraud than building new features. And when you finally implement "verified purchase" requirements? Sellers revolt because their legitimate customers can't leave reviews from past sales.
The dispute resolution black hole
Nobody plans for disputes properly. You assume sellers and buyers will work it out. They won't.
- Every dispute becomes a three-way email thread
- Support tickets reference other tickets in an endless chain
- You're storing gigabytes of photos of damaged items
- Sellers and buyers both bombard your Twitter
- You're basically running a small claims court
The technical debt accumulates fast. Your support tool wasn't built for three-party conversations. Your database wasn't designed to store evidence files. Your team wasn't trained to be judges. Most marketplaces end up building an entire custom dispute system, but by then you've already lost your best sellers to platforms that handle this better.
The pattern
All these problems have something in common: they're human problems disguised as technical problems. You can't solve them with better code or faster databases. They happen because marketplaces are trying to create trust between strangers at scale.
The successful marketplaces aren't the ones that solved these problems perfectly. They're the ones who accept that these problems exist and built their entire experience around managing the chaos, not preventing it.
Your v1 doesn't need to be perfect. But it does need to acknowledge that these issues will happen. Build in the flexibility to handle edge cases from day one, even if you handle them manually at first.
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