A consultancy is a service oriented business. As consultants its our job to make our clients happy, but more impotently make their businesses better for hiring us. For clients to hire consultants and give them access to their code requires trust. They are passing off their baby and golden goose to us. If they don’t trust who they have hired, they’ll get spooked and take their business elsewhere.
Thats why even if you’re the most competent programmer in the world and you have brought back dozens of projects back from the brink of death, if you don’t look and act the part none of that matters. The problem is that clients can’t see into your head. They don’t see the knowledge that is there or the skill you wield. They see you, how you dress, how you talk, and how you carry yourself.
If you don’t look and act the part you will leave a bad impression, no matter what. Egos serve no purpose when dealing with clients.