Unethical? If your customer truly believes that you have conducted an exhaustive study of every comparable business in a 100 mile radius, analyzed their business practices, interviewed all their past clients, and hired a consultant to evaluate their work - where the heck did you find them? Otherwise, anyone knows "we're the best" means "we believe we're the best and that's important to us." If someone doesn't believe their the best - whether it's an employee or a vendor - then they're wasting my time.
Come on, what did Ghostbusters teach us? "If someone asks you if you're a god, Ray, you say yes!"