Careful not to over promise, many professionals miss opportunities for lack of assuring the prospective client of their firms ability to deliver. You may be reserved in your manner, but that does not mean you shouldn’t be passionate about the capabilities of your firm and its fit with the client organization. Everybody seeks to be affirmed in their decision to buy. That’s your job.
If you believe the client is making a good choice by selecting your team and your firm, tell them so. If you don’t believe in your products and services, why should the client?