We used SF Enterprises, which is a Tongan family-run business. We had stuff shipped from all over the U.S. directly to SF Enterprises' LA office, with Shango's name on it. Roger and Amy used their 8 hour layover in LA to go to the warehouse and pack the crate up (not absolutely necessary, but they wanted to ensure their expensive new solar panels were properly packed).
The shipment went by freighter to Nuku'alofa, Tonga, and SF Enterprises in Nuku'alofa then delivered it by ferry to Vava'u, where it was delivered to the Customs shed. Roger had to do a bank transfer to SF Enterprises in the U.S. before they would ship the goods up to Vavau. On arrival, we also had to pay some kind of paperwork fee to the shipping company, Reef Shipping.
We used Linda from Jetsave Travel in Neiafu (also the Fed Ex agent) as our Customs Agent, to get the goods released from Customs. An agent is not absolutely necessary, especially if you have invoices for EVERYTHING you've shipped, but there is a lot of paperwork involved, in Tongan. Linda helped a lot with the voluminous paperwork, and getting all the miscellaneous stuff (which we did not have invoices for) cleared, and we felt that her fee was very reasonable for the effort required on her part.
Most of the parts were considered 'repair parts', and covered under the "Yacht In Transit" rule (no duty in Tonga). Books are also duty-free. However, some things, like the dive gear, clothing, and food items, were dutiable. Dive gear ended up being taxed at almost 40%--but there isn't any dive gear available here, so there was no other option. Fortunately, we had helped Roger buy used stuff, so the tax was on less-than-retail prices. Other items, the duty was only 15%.
Some items--like tobacco, are really heavily taxed. We shipped 4 1-pound bags of pipe tobacco for Larry of the Ark Gallery in the shipment. These cost $84 in the U.S., but the Tongan duty was $240 pa'anga (about $150 USD). We left them with Customs in Larry's name--for him to decide if he wanted to pay or just leave it there. We could probably have brought some of the tobacco in our luggage duty-free had we known it would be taxed separately--like everywhere else, you are allowed a limited amount of stuff in when you fly in, duty free.