That depends on what you have agreed with your customer. If the customer wishes the app to be released under a new developer name then he will have to bear the costs as well. That's how I would handle it.
Or your Customer have already has its own account.
I have a Account for my "Company", There I publish my apps under my name, but if I now have a special project, which needs its own publisher name, then I have to create another account.
But maybe another member in the forum has a different opinion and can teach me a better one.