can you haggle contract rates

[DirtyOldMan]

RULE 1: Never post when you're under the afluence of incohol.

[Oscar]

The agent might not know the rate

I think agents often have to put a price on their offer. They might not know the best rate to put (But they know the marked better than you). If you ask more, they will probably put a higher rate to their client, and perhaps squeeze their margin a bit (I would guess).
Sometimes the client might come back and ask for a lower price. So if the agent ask you "What is the lowest you can go" or something like that, ask exactly what they mean. (If you can keep the rate high until the client responds, you are in a better position)

[Spartacus]

If the agent asks you what is the lowest you can go, and you answer, you will find pretty quickly that by an amazing coincidence that is the highest the client is prepared to pay.