This really is quite an interesting discussion.
The issue ultimately comes downs to different people's interpretation of what is acceptable in the way of packaging for a bass. I have bought three basses of eBay - I collected one and had the other two posted. One was a cheapy and just had cardboard wrapped around it with some packing tape, no suprises that one of the machine heads had been snapped off by the time it arrived. With the other (mid priced) bass, I specifically asked the seller to ensure it was well packaged. They sent it in a reasonably well padded soft case with a little bit more bubble wrap around the neck. Now, if I was going to send a bass like that I would completely stuff the case with bubble wrap and cover it in fragile stickers. The softcase was not mentioned in the advert so this was a bonus, but the bass did suffer a couple of small knocks to the body (which was previously mint condition). So the seller has a different interpretation as to what 'well packaged' mean compared to me.
I think the only thing you can do is to agree in some detail with the seller as to what you would deem to be acceptable packaging before you bid. If you then win/buy the bass and it is shipped differently then you have a string position to make a case.
Just my thoughts.....