What should the assessment answer?
Ask where the cabinet would go, whether there is room to remove the filter for future care, and how it would fit the existing return-air path. Request the exact cabinet and replacement media, rather than accepting “four-inch filter” as a complete specification.
We recommend having a qualified professional check the proposed arrangement against the furnace's airflow requirements. The evaluation should include the blower, the existing system resistance, the proposed filter's resistance, and the physical installation. A larger filter is a design option, not a guarantee of better operation in every home.
If the proposal requires return-path or other installation changes, get those requirements, costs, and the responsible provider identified separately. Do not assume the cabinet price includes every alteration, or that a furnace replacement is the only way to make room.
Compare the benefit with the work
Ask what problem the change is intended to solve. Is it replacing an unsuitable rack, reducing frequent changes, or improving particle capture with a compatible product? That purpose helps you compare the cabinet with keeping a supported filter in the current arrangement.
A sensible proposal explains the benefit, the operating basis, the total work, and the future filter cost. If the provider cannot establish compatibility or reasonable service access, keep the existing approved arrangement while considering another approach.
Do not stack thin filters or modify the cabinet yourself. Your next step is a written assessment of fit and airflow, followed by an itemized proposal if the change is supported. An older furnace can be evaluated fairly without treating its age as either an automatic yes or an automatic no.