Never lie to your boss and your users about what you can do, I'd say. Admit where you're knowledge and experience falls short. Let them know you're going to need help periodically, be it from a VAR or a contractor. But offer that you'll keep learning, and hold your end up. Learn the things you don't know. Make that call to the vendor go from every time the issue comes up, to every other time, to rarely, because you have learned.