I've never had a problem with UPS, but I only deal with one Customer Center, never have been to any of their other shops, but they don't accept firearms everywhere as stated in their regs, same for ammo too.
Tim
You can ship a firearm (excluding handguns), from a UPS daily pickup account, UPS On-Call Pickup, One-Time Pickup, or a UPS Customer Center. Note: Firearms are not accepted for shipment through UPS Internet Shipping, UPS Drop Boxes, or at The UPS Store or any third party retailer.