Log into your account in the store (most copy shops have an Internet connection) and show them:
1. The official e23 notice that you have permission to make a single hardcopy, at:
http://www.warehouse23.com/downloads#copyshop
2. Your account list, showing that you paid for your PDF (or received it as a comp copy, for authors), at:
https://www.warehouse23.com/account
(If your shop doesn't have net access, print a copy of your receipt, which was emailed to you, and a copy of the FAQ, above.)
That's all the shop should need to cover themselves legally.
If (for some reason) that's not enough for your copy shop, email
e23orders@sjgames.com with the details of what you're trying to get printed, and we'll send you an email granting official permission.