Hi.
No harm will be done, and if something happens, You always can try and sue them.
All it would've taken is one piece of paper, stating that the bass and the case was fumigated beforehand and You wouldn't had to worry.
Don't know if You're noticed, but there's a few species in your dry continent that really doesn't belong in there

.
Some came by accident, some were brought intentionally. Want some more?
Your laws about import restrictions and material handling are trying to fight that.
Many moons ago I worked in a company that made agricultural equipment, bale-wrappers to be precise. Two of our largest clients were in AU/NZ area and we had to deal with those restrictions. Unfortunately money often comes in the way of reason and instead of using the required pressure saturated wood (expensive), the powers to be decided to use untreated 2*4 stock to build the supporting structures between the different macine parts. Both engineers of the company, me includced protested, but no success.
When the container reached AU customs they gave only one option: the container has to be shipped back, UNOPENED. Great.
The AU dealer did something, don't know what, but he managed to arrange that the container was gassed IIRC, the doors opened and as soon the wood bits came out they were burned in a bonfire, later that whole container was thoroughly fumigated. DID cost us A LOT.
Just my 0.02€
Sam