When one does not find a tracking number updating on usps.com (domestic cases only) and its been over a week, then its very likely that the package is stuck up in some place on its route. This situation arises doubt in the buyers mind and sellers get worried. But instead of getting upset with each other or distrusting here is the simple solution for it-
On hearing the options ask for customer service (possibly you would have to say so couple of times). Also keep hitting the 0 (zero) button on the phone and eventually you will get someone on the phone.
Ask him/her to put a search on ur package saying you cant see any update on their website. Provide the tracking number to them. They sometimes can see some sort of update on their system and if not they open a search case and get back t you within 24 -48 hours.
In 99% cases they do track down the package and you recover it. This is often see during this time of the year when they are most busy.