Here in Canada we hear this complaint often.
There is very little you can do.
The customs brokerage fees charged by couriers like DHL, UPS, and FedEx are very high and are not disclosed to your seller (who will not be paying them, he pays only for the shipping with the money you give him), or to the buyer/importer.
These are charges for a service, so you can inform DHL that you do not need the service and that you will broker the item yourself. I am not sure what the Bolivian rules are for this, but you will certainly need photo ID and proof of address.
Please note, that even in Canada, this can take some time and a lot of paperwork. Will the saving in money be worth the labour?
As a courtesy, you should inform your seller about your problem. He can't do anything about it, but it may lead him to choose his shipping service more carefully in future.