Need opinions on form design

I need opinions so I can convince my client that what he wants is the
wrong thing. There is a sign up form, and if the user has a business
card from the referring agent, then the person should put the agent's id
number in the form.

I think that information should be put at the end of the form, not the
beginning. I think that asking for a referring agent id might be
confusing, especially if the user does not have an agent's business card.
But, my client says that the agents want that field...

Need opinions on form design