As a generalization, the taxidermist your items are taken to for processing, either just dip/pack & ship or whatever level of work you want done there, have shippers they commonly use to get your items to the US port of entry. Unless you know are aware of and want to use a specific Africa to US shipping agent, it's likely just a good idea to use the agents the taxidermist is familiar with.
There are several US based receiving companies that will clear your items thru US Customs and USF&W and then hire/coordinate the US based shipping/freight forwarding company from the port of entry to your location. Two of these are Coppersmith Global Logistics and Flora & Fauna and the Wildlife Gallery if you have your final taxidermy work done with them.
Yes, it does seem as Bawana338 said, it is is pretty common that the majority of ALL business that I've had experiences with in RSA, Namibia and Botswana provide some level of extra payments back to the referring business. Seems 10% or less is the normal amount.
On the flip side of that, is it really that much different than US companies/businesses that offer referral/finders fees or promos of referring a friend and get a discount on your bill etc. Not trying or intending to support/justify any of it. It is just what it is.
