I must be living in a fools' paradise, because I've had a number of guitars shipped to me and by me by UPS with no trauma yet.
Of course, anytime you ship a guitar, by any medium, you want to take the essential precautions:
- Ship it in a hard case, an archtopped hard case if at all possible.
- Detune the strings.
- If it isn't a really snug fit in the case, pad around it with rags or whatever. (No plastic touching the finish!)
- Pad with more rags underneath and above the headstock, to ameliorate whiplash effects.
- If the end pin can be removed, take it out and put it in the accessory case. It acts as a splitting wedge if the instrument gets dropped or set down hard on its big end.
- Pack the case in a box, with plastic peanuts or wadded up newspaper to immobilize it in the box.
- Be wasteful of tape in sealing the box. Taping along the edges of the box to reinforce them is a good idea.
- Don't bother marking it "fragile." It's as likely to be considered a challenge as a warning.
Having made that brag, I will probably ship FedEx or USPS next time, on the theory that I've used up my luck and may have angered the gods.