As Grumps stated, I have always treated Geico the same as all the other motor clubs, credit card up front at commercial rate only. A couple weeks ago, I had a dispatcher take the time to explain how their PO/billing system works. I decided to take a chance, quoted commercial rate and accepted a PO. I submitted an invoice online and requested to be paid by check, instead of giving them access to my bank account for a direct deposit. The check arrived within a week for the correct amount. I have to admit I am impressed.
Keep in mind that I do not have a contract, and have no intention of even talking to them about that, but it seems that they do pay their PO's promptly.