From Mexico here.
I've sold a lot of things, national and international. I usually offer tracking number with the packages I send ($2 US), understanding that not asking for it is a risk buyer is taking.
When I buy international, depends on the price with and without tracking, and the value of the things I'm buying to know what service I'll ask.
As far, only one item has been "lost" (2008?), but that was a really... weird story I can't really understand still. Two times I've asked for tracking number from US, but arrived in the same time, and a lot of money to ask for it, the others I haven't asked for tracking number and just be patient with the delivery.
From what I've sent, all have arrived safely, only a little late sometimes, but package being on the country where it should be.
Mexican PS tracking service 'stops updating' when the parcel lets the country, which only takes at most one week to left, but somehow can be tracked asking directly on the buyers country when given the tracking number to ask.