If the shop asked you to pay in full up front (which you did) and forgot to charge you sales tax then that is their ovesight, not yours. Tell the manager to charge the tax to whoever failed to correctly bill it to you DURING the transaction.
As for the decal screw-up - sounds like a communication error between your shop and Waterford. I've been to the Waterford factory numerous times and can tell you that the request for no decals would be on the build tag, and that tag would stay with the frame from order through to shipping.