International Excess baggage to Macedonia

Hello and thank you for responding to my inquiry into international excess baggage to Macedonia. I must travel to Macedonia next month on business. My journey will begin at Riyadh, Saudi Arabia. I am also required by my employer to carry with me many items so that I may display them to potential customers. I have been informed by the airline that I am due to fly that there will be limited baggage shipping availability for the flight that I am scheduled to take. Therefore, I am seeking the services of a company who can provide excess baggage shipping services. Please explain how your excess baggage shipping services work. Do you charge by the weight? I have heard of volumetric weight? What is that and do you use that to base your shipping charges on my excess baggage? Is it possible that I can prepay my shipping charges? Where do I drop off my baggage and where do I pick it up? Is it necessary that I label my baggage any differently than I would if I were to ship them with the airline?