I was buying some things recently to build a 3d printer, so the following advice applies more to smaller imported items.
The printer parts were extremely difficult to find here, some impossible, and everywhere I went to buy it was always the same scene. A guy or couple in their 20's, operating out of a small business or from their house, buying and selling full time. I asked where did the stuff come from, and it was always from China, and being sold here at about a 50% markup. This advice is an outline of what I learned, asking numerous such vendors their advice.
- Order from China, because they tend to have low-cost or free shipping, good prices, and more of a tendency to mark a yet-lower price in the shipping paperwork.
- If you buy from a china vendor with a good reputation, they are in the buying/selling business, not in the business of ripping you off. There might be occasional problems with quality, but they're not likely to just take your money and run.
- Customs is in the business of getting all the money they can, but their resources are not limitless. To greatly increase your chances of the package passing custom-free straight to your door, follow these rules of thumb:
- Order amount less than US$100
- The smaller package dimensions, the better. (this seems to help it get here faster too, as the low cost china shipping is also low priority to get loaded on the plane. There will more likely be room on the plane if you have a small package)
- Weight, best under 500g. Up to 2Kg is possible.
- If the vendor is putting a lower declared value than the actual value, best it is not something common. If the custom agent recognizes it to be a cell phone, bicycle part, etc, something common, they're going to know the real value.
- Use regular air mail, china post, usps, etc, NOT UPS, Fedex, etc. (I believe this also relates to pickup in retiro vs EZE if it happens to not pass customs, correct?)
Some interesting sites for this type of purchasing: ebay, dx, aliexpress, dhgate