The problem is not USPS, it's Parcel Post. That's USPS's cheapest service. Priority Mail works fine. I have sent well over 1,000 parcels via Priority Mail with only one loss, and that was an apartment dweller and you know how that rolls . . .
The issue with Priority Mail and guitars is that it's way expensive compared with UPS. Once you get above a certain size, you go UPS and not USPS (unless you are a cheap bastard and select Parcel Post).
USPS does not advertise Delivery Confirmation as tracking, because it's not. You do get better info with Priority Mail than Parcel Post, but it still tends to lag reality.
Bottom line is a git should be shipped insured AND properly packed anyway . . .