CISOs, what's the secret ingredient to a healthy and productive relationship with your cybersecurity vendors?

Continuous feedback and an open discussions about your needs, software features/updates needed, things that can be improved in the support etc.

Plenty of coffee dates. :) But on a more serious note you as a CISO need to know what you need and vendors need to have patience and understanding that not all technologies are relevant or needed for a particular organization. Pitching all the products your company offers doesn't make a lot of sense most of the time because there might be overlapping technologies in use and worst case scenario you end up looking desperate as a vendor if you pitch too many things.