R4 — Never rent mission-critical data infrastructure when the vendor can reprice unilaterally; keep the path to a free alternative warm

Rule: When recommending paid data infrastructure for a mission-critical dependency (mapping, lookups, geocoding), always preserve the path to a free alternative. Never let a client depend on a vendor that can unilaterally reprice them out of business.

Why: Google Maps 2018 (Google Maps July 16, 2018 pricing overhaul — per-1,000 map-call rate from $0.50 to $7; free map calls from 25,000/day to 28,000/month) and March 2025 (Google Maps Platform restructured pricing March 1, 2025 — replaced the universal $200/month credit with per-SKU free caps and Essentials/Pro/Enterprise tiers) are the canonical examples. StreetEasy switched to OSM when Google would have cost ~$300k/year (StreetEasy switched from Google Maps to OpenStreetMap after calculating Google would cost ~$300k/year; Foursquare also switched). The smaller the SMB, the more devastating an unanticipated rent increase.

How to apply:

• Mapping defaults: use Google when free quota covers usage, design the integration so OSM/Mapbox is a configuration change, not a rebuild.
• Document the cost ceiling at which the alternative becomes preferable.
• Review the vendor pricing model at scoping time, not after first invoice surprise.