I raise the money I use for my astronomy habit by buying, re-furbishing, and re-selling old Press cameras and lenses on eBay. Over the past twelve years I've shipped more than a thousand items all over the world using USPS. Only once was an item damaged (and I'm convinced this was done by a buyer who 'changed his mind'; the package -- a pretty expensive lens -- looked like it had been stabbed with an ice pick, and the buyer was not a pleasant person to deal with, even before the package was received). No item has ever been lost.
As others have said, USPS recently changed their tracking, and it is now excellent.
The one problem I've had is with International insurance. The maximum amount allowed by USPS is usually pretty low (usually under $1000), and it varies from country to country. My Postmaster says that the limit is not set by them, but by each country. It's not often that I sell something for that much, but when I have, and buyers wanted to pay the extra cost (usually more than double), I've used another shipper.
I use USPS exclusively. When insurance to a particular country won't cover the product, I split it into multiple boxes. Because it reduces the weight of each box, it also reduces each package's shipping cost. Multiple boxes cost more to ship, but insurance is important.
Of course, I ship primarily smaller items. What I said wouldn't apply to larger or radically more expensive items.
When I bought a high-end laptop a few years ago, it was FedEx'd to me overnight
from China! Somebody ate some expensive freight, and it wasn't yours truly.