I'm not sure who pays commission in Arizona. In Illinois, the seller pays the commission to the listing broker. The listing broker then pays a cooperative commission to the buyer's broker.
If you were trying to work out an arrangement, it would have to be between you and the broker, not the agent. The agent isn't the one who can approve a highly unconventional agreement. A listing agreement is a contract between the seller and the broker. The broker employs agents (who may be licensed brokers themselves) to market services, including buying and selling real estate.
If you're a seller, please understand that your agent has marketed your property at their own expense with the expectation that they will be paid when the transaction closes. In other words, they've done their job. As a seller, you aren't waiting for your money from the title company or escrow agent after closing...and it doesn't come in installments. The attorney gets paid at closing. What's more, your broker has to pay the buyer's broker. There really isn't any leeway here.
If you have no proceeds from the sale of your home or are bringing money to the table in order to close, then you can sell short (which would require bank approval and has severe credit implications) or you can try negotiating with your broker on their commission. Some will, some won't...but, choose wisely. We're not all the same and we're in a business where most times you "get what you pay for"...good and bad.
My advice is to be upfront about your situation when you're interviewing prospective agents. By interviewing several, you should have a very good idea of what your home's selling price will be. Work out your closing costs from that number and see where you are. Ask for the agent's best commission rate and make the most informed decision you can.
Typically, however, as those before me have stated, the agent is paid at the time of closing, or within a few days of closing, once the money has been filtered through the agency, and comes back to the agent.
Jen and Mark Bowman
Keller Williams on the Water