Trustless escrow contracts for a marketplace platform

The client runs an online marketplace where buyers and sellers who do not know each other need a reason to trust a transaction. Removing that trust gap is the platform's core value, and escrow is how it delivers it.

They wanted on-chain escrow that would hold a buyer's funds safely until delivery was confirmed by both sides, so neither party had to take the other on faith.

In a peer-to-peer marketplace, a buyer risks paying for goods that never arrive and a seller risks shipping goods that are never paid for. The escrow contract sits in the middle of that standoff and has to be trustless enough that both sides accept it.

The hard failure mode is funds getting stuck: a dispute or an unhandled state that leaves money locked in the contract with no path out. On an immutable contract holding real balances, that is not a bug you can quietly hotfix.

The platform needed escrow that handled confirmation, disputes, and refunds cleanly across every path, with confidence that money would always be able to move to the party entitled to it.

We built the escrow in Solidity on OpenZeppelin foundations, modelling the full lifecycle of a transaction so buyer funds are held until both parties confirm delivery and then released deterministically. Settlement in USDC gave both sides a stable-value asset they could reason about.

We hardened the contract with Foundry-based fuzz and invariant testing, deliberately hunting for the states where funds could become trapped. Invariant testing is precisely the tool for proving that money always has a valid exit, no matter the sequence of events.

Every dispute and refund path was exercised until we could show that no reachable state left funds stuck. That evidence is why the marketplace could stand behind the escrow to its users.