Most vendor checklists are really feature checklists in disguise: does it integrate with X, does it support Y language, does it have Z dashboard. None of that predicts whether the vendor relationship will still make sense in eighteen months.
Ask about data residency directly, not "is my data secure" — get the actual region the data is processed and stored in, and whether that can be contractually guaranteed, not just claimed on a marketing page.
Ask for the export format in writing before signing, and actually test it during the trial period. "We support data export" and "here is a working export of your trial data" are very different levels of confidence.
Ask how pricing scales specifically — not "is it affordable" but the exact per-seat or per-call rate at 10x your current volume. Vendors size pilot pricing to look attractive; production pricing is where the real number lives.
Ask what happens when the model is wrong in a way that matters — refund policy, human escalation path, and who is liable. A vendor without a clear answer here is telling you something, even if they don't say it directly.
None of these questions are hostile. A vendor confident in their product answers all four without hedging.