I've shipped international before and the buyer told me he could track the mailing using the Customs Form number.
I just looked at a Priority box sale on eBay that I sent to Japan, and it automatically got the Customs Number recorded on the sale. The number in this case started with "LJ". domestic tracking numbers are always a long string of numbers.
My own rules for selling on eBay:
Always, always, always, make sure you are going to get a tracking number. Priority it's free, 80 cents if Parcel Post. Darned well worth it. Set your shipping cost high enough to cover it and packaging. eBay automatically records the tracking number on the sale information.
Always print the eBay invoice out and place it in the package. USPS advises that both addresses be placed inside all packages, that way if the outside address is ever destroyed to where they can't deliver, they will eventually open the package and attempt to determine where it was supposed to go, and eventually deliver. (Told to me by a Postal employee).
Always ship thru eBay, they/you get a discounted rate for some, such as Priority packages. Plus they automatically record what I just said. It's online for you after that on your eBay account. I have to suppose that eBay, already having this information, would help you out if a dispute arises.
eBay notifys the buyer automatically with your shipping information, including that tracking number, right after you shipped if you use their shipping services.
I personally think eBay's and PayPal's services are pretty darned slick. You should take advantage of them as they are "free" from the fees you pay them.
Pay attention to eBay "Messages" after the sale. If something goes wrong, the buyer will most likely contact you that way, since they don't have your email address. I had one "wheres my item" message. Turned out they moved and did not update their new address in PayPal. Unknowing, I mailed to the old address since it was automatic. We figured it out and I got Positive feedback from them anyway.
Like I said, just my own personal "rules". YMMV as always.
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