The sandbox filtered every input to match the vendor's ideal schema before any processing began. Your approval rested on throughput numbers that only exist once that filtering step is already complete.
Production traffic arrives with the duplicates, the nulls and the schema drift your upstream systems have accumulated over years. The moment the connector opens to live data the reported latency doubles and the error queue starts filling.
Build-versus-buy comparisons collapse when the buy side hides the custom mapping layer required to reach parity. The vendor quote covers only the core licence; the mapping work gets classified later as an integration variation.
Internal teams then spend months recreating the exact transformations the demo concealed. The original business case never accounted for that effort because the sandbox evidence made the product appear plug-and-play.
Craft proof requires running the candidate against an unfiltered slice of your current production load, not a curated extract. Anything less simply shifts the cost from the purchase order to the subsequent change request.
Procurement teams that demand this test before sign-off surface the real integration debt while it can still influence the price or kill the deal. Teams that skip it discover the debt only after the first invoice clears.