USPS is notorious for taking forever in the event a claim is filed which brings to the fore my first point. Avoid USPS unless using priority mail and limit that as well. Priority mail only for small light weight packages--ship anything over 10 lbs or so via FEDEX or UPS.
There is no difference in quality or reliability of service using FEDEX or UPS , while one may cost less that doesnt really matter in terms of how well the carrier processes your package. There are all kinds of stories online re/poor handling to put it mildly. I have been selling on Audiogon since 03 and the first order of business is pack your item as if it may be tossed off a train as its quite common for packages to fall off a 6 foot high conveyor at the hub. As far as your delivery goes it would be quite a rare situation for a buyer to not contact a seller re/non delivery. Likely he got it.