The custom hassles depends on which carrier the amazon seller uses. DHL and UPS can be problematic. UPS has asked for me to mail my passport to them a couple of times Then they want a description of the item, in Thai also. This in spite of them sending an attachement with a description of the item. A picture of the item. And a sales receipt. Customs is not the problem. It is these companies. In my experience the best way if possible is to use regular postal service.
They will also tell you that the item can not be returned if you don't give them what they want. I refused to mail my passport to them. One item was so valuable I ended up having my niece go to their office at the airport with my passport. The other one was a box of candy canes. I just let it die in delivery. After I explained everything to amazon they did refund the money to me though.