Air sealing belongs in the scope
Ask where and how the opening will be insulated and sealed. Product performance alone does not establish the performance of the installed assembly.
Inspect more than appearance
During the walkthrough, operate locks and sashes and request care instructions. Ask who handles a later issue and how labor coverage differs from manufacturer coverage.
Plan for your property
A warmer room is not always a window problem. Look at drafts, shade, orientation, and installation details together. Compare documented product ratings instead of relying on a promised energy saving.