I've never really had any bad luck with couriers, a couple of times things have happened but we all make mistakes / have accidents sometimes.
Being down in Cornwall everywhere is a long way so I use couriers a lot.
I've recently bought a bass on ebay and arranged for a courier to collect it. North Yorkshire to Cornwall ยฃ12.50 including insurance as an instrument. This was DPD booked through Eurosender using the forum discount, 2 days door to door.
I once received a bass wrapped in a single black bin liner, no damage amazingly, someone must have been extra careful with that one.
Worst I've had was a Squier Bass vi from GAK, bent control knob, could've happened at any point in the supply chain, quickly returned and the next one was delivered in perfect shape, and a doublebass from Gedo which arrived from Germany with the fingerboard popped off, possibly courier handling, possibly manufacturing error as it was only where the glue let go.