The everyday problem
A vendor may describe several ways to adapt a platform without making their long-term implications clear. A standard setting, a supported extension, and bespoke code can create different maintenance responsibilities. Those differences matter when the platform changes.
A practical approach
Ask which requested behaviors are standard, configurable, or custom. Clarify who maintains custom work and how it is tested during upgrades. Include the cost and ownership of future changes in the comparison, not just the initial implementation effort.
Try this with your team
Classify five requested capabilities by delivery method. For each custom item, identify the maintainer and the plan for validating it after an upgrade.