Hi Meredith!
I do lots of custom orders and if someone settles on something, I generally go ahead and create the listing and send it to them in our Convo/email. Sometimes it gets tiring going back and forth (not for me but I fear that it does for my customer), so I just create it and let them know that it's waiting there for them. What's the worst that can happen? You lose 20 cents. I'll usually say something like, "Here's your custom listing and it'll be waiting there for you when you're ready. If you've changed your mind, that's not a problem at all, just let me know." Then thank them for working with me. Good luck! Here's hoping you seal the deal!
Nicky :)
Edit- I read your original post and it seemed you were asking whether or not to go ahead and create the listing without the official nod from the customer... However, like the other gals have said, I NEVER order or manipulate materials until the listing is paid in full.