The most worrying sentence in a vendor demo: "Yes, we can customise that"
The sentence in a vendor demo that should worry you most is "Yes, we can customise that."
It sounds like flexibility. It is a fork in the road, and both directions cost more than the demo suggested.
Down one path, the customisation is real and the vendor does it. You now run a version of the product nobody else runs. Upgrades break it. Support tickets get the reply "that's a customisation." The two people who understand it are on the vendor's payroll, and the day they leave, so does your ability to change it. Three years in, you cannot move to a competitor because the competitor sells the standard product and you no longer use one.
Down the other path, "yes" meant "a partner can do that" or "it's on the roadmap." The feature you bought on the strength of that sentence arrives late, priced separately, or never.
The question to ask in the demo is not "can you" but "have you, for a customer like us, and can I see it running." A customisation that already exists somewhere is a feature. One that would be built for you is a project, and it should be priced, scoped and owned like one.
The uncomfortable part: the customisation you are asking for is often a process you should change rather than a product you should bend. The vendor will not tell you that. Saying yes is easier and it bills.