When should I build a custom extension vs buy from Marketplace?

Buy when an existing Marketplace extension covers 80%+ of your need with reasonable config — it’s nearly always cheaper than custom and someone else maintains the upgrade path. Build custom when (a) no extension solves the problem, (b) you need it to integrate tightly with proprietary systems (ERP, PIM, custom checkout flows), (c) you’re selling the extension itself, or (d) the closest off-the-shelf extension would need so much customisation it’s cheaper to start clean. Our spec audit ($499) gives you the buy-vs-build call in writing before you commit.