I ship quite a bit internationally using the above methods and the only service that provides real tracking is Global Express Mail BUT I have put in the Global Priority Mail number and even the customs number from the green customs form (for airmail letter post) and was able able to track it to a point (Not always all the way through). There are some very interesting posts on the Ebay discussion boards about using the custom's form number to track to countries like Canada (I can find those links for you if this is how you sent it).
Let us know how the parcel was sent and maybe we can help to some suggestions on what to tell the buyer. Myself, I do not tell the buyers up front that I can see any type of tracking unless there is a problem but found out that I can track packages when a customer in Germany stated that she did not get her package and I could track until it left JFK airport and miraculously it showed up at her door the next day (hmmmmmm
Let us know!
Marcia