On the job training should be proficient. Obviously, guitars can range from low $ to high $$$$ in a hurry. The guitar store very likely has specifics on packing and on training so I would think they would need to supervise and teach the correct procedures.
Hope this helps!!
Also, apologies as this isn't my primary field of knowledge/ experience. Although I do have experience experience in the packing/shipments/etc. Field. Take care. Be safe. Good luck.