Shooting a commercial for a pitch is not just costly in terms of money, it costs you in terms of people. You will throw a couple of creative people and several producers against an effort that will ultimately prove futile. The rest of the creative department will click into half-speed, since it appears their efforts will be overshadowed by a full-blown television advertisment shot and finished. They’ll stop trying.
Shooting a commercial means you’ve missed the point: the point is to sell your advertising agency, not a single television commercial. A little film or an idea video or something, fine. But a TV commercial that you presume the client will fall down and die for. You’re crazy.