Good Lord. BB-7s front and rear, and he isn't satisfied with the braking?
Rick, it sounds to me as if a little riding instruction might be in order. You know, that old axiom about, "The customer is always right" .....it's a crock. In fact, they're usually not and they often need more information. Have you personally ridden this bike? Do the brakes perform for you? You're the builder and the knowledgable one. Instruct the guy on proper braking and he might go away happy.
I'm of course assuming the Avids are installed and adjusted properly. They are the quintessential brake for a bike and rider weight shouldn't make them less so. Rider misuse however can compromise any braking system.
Tom