[pjc50]

I think the ways to approach it are:

- this incurs real costs, so we should charge for this. (The charge doesn't have to be related to the costs! But if you're doing something extra there should be an extra line on the invoice)

- this customer wants something that other customers don't have. There's all sorts of real-world services where you can pay to board the plane first or get to the front of the concert. These may be several times more expensive than the regular service. That lets you phrase it in fawning terms ("you can join our Super Elite Ultra Platinum Preview Fellows") and thereby extract much more money.