Personally I wouldn't post a bass, if the buyer can't collect it or meet me then tough .
I'm selling my TRB6P, and I've had 2 offers from people wanting to buy it, one was in the West Indies of all places, the other in France.
It's too risky for me to ship it, if it gets trashed or lost then it's me that loses.
I have a YP railcard and will deliver for train fare, which is probably cheaper than insured postage and a lot more reliable.
Are they saying they'll post it but the buyer has to arrange shipping and insurance ? I think that's fair, as long as the seller packages it and takes photos or videos the packaging for their protection.