What still has to be true after the sales pitch is over?
A good demo proves a product can do something. It doesn't prove your organization can run it, that everyone understands their responsibilities, or that the commercial terms will still make sense once your needs change.
A good selection process starts with the business outcome and how you actually work. The criteria should separate must-haves from nice-to-haves, flag the assumptions that need checking, and name who will own adoption, administration, support, security, and renewal.
Our job isn't to pretend every option is equally good. It's to make the basis for the recommendation clear, and keep the vendor's claims separate from what's actually been verified.