Can I insist that all consents be obtained in writing, not just verbally confirmed?

Yes, and doing so is good, standard practice rather than an unusual demand. Requiring that any required third-party consent — a landlord's consent to a lease assignment, a supplier's or licensor's consent to assign a contract — be obtained in writing, and delivered before closing, gives you something concrete and provable rather than relying on someone's verbal assurance that "it's fine" or "they said yes on the phone."

A verbal consent is genuinely difficult to rely on later: it can be misremembered, denied, or simply never actually communicated to the right person at the other business, and if a dispute arises after closing about whether a consent was properly given, a written record is far more useful evidence than someone's recollection of a conversation. Building a written-consent requirement directly into the closing conditions also gives you a clean, objective standard for whether that condition has actually been satisfied, avoiding exactly the kind of "did we get consent or not" argument that can otherwise derail a closing.

This is a small, low-cost drafting choice with real practical value, and it's the kind of detail a Treadstone business lawyer builds into closing conditions as standard practice.