Did you actually state a deadline for when you would need that PO to extend Al's time there? The "customer mentality" tends to be "We are throwing these guys business, they should be honored to grovel for it and jump to it when we snap our fingers."
If you had set a deadline for the PO, then by all means charge extra for the "rush order" (hey you order overnight shipping with Amazon you pay through the nose, right?). Otherwise, if they've pulled this stuff before, and you haven't said "here's when we need the PO by and here's what's going to happen if you don't," you could risk alienating the client further. |