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Common hidden costs: 1. Developer setup: GTM server-side advertises $21/month but requires $5,000-$20,000 developer implementation 2. API changes: Facebook updates CAPI requirements quarterly. Each update = 2-5 developer hours debugging 3. Platform deprecations: Google sunsets API version. Rebuilding tags = 10-20 hours 4. Knowledge dependency: Developer leaves, new one must learn custom setup = 20-40 hours 5. Scaling failures: Traffic spike breaks container. Emergency fix = 5-15 hours 6. Authentication expiry: Tokens expire, tracking silently fails. Finding and fixing = 2-5 hours **Budget extra $3,000-10,000/year for "tracking broke, need to...