Our efforts to deliver double basses by regular mail resulted in numerous refusals from local postal workers, and even the postal delivery service wasn't really up to the volume and weight of the instruments. In short - we were unhappy with the whole situation... ;-) But seriously, we've always delivered double basses by freight. The basses are packed in approximately two-meter-long double bass-specific boxes. These boxes are strapped vertically onto pallets and delivered to you vertically by truck.
Please make sure that the bass actually arrives with a pallet and inspect the instrument in the presence of the delivery driver for any transport damage. Any damages caused during transport must be reported to the truck driver immediately. The driver is obliged to wait until you have inspected the bass.
By the way - delivery within Germany is free of charge!