As a buyer, you cannot make a seller into a better shipper.
I never agree to pay for shipping. If they want $2000 plus $100 shipping, I offer $2100 and they ship it. this eliminates any ambiguity who is responsible for shipping. Until you recieve it in good condition, the seller is responsible. When you give advice on shipping or pay extra, you are muddying the waters.
I always make it clear that shipping is thier responsibility, that I am in no hurry so take whatever time needed to ship it safely. that is all I say.
When I am the seller, I operate the same way. I take responsbility for shipping. I've done a lot of shipping, plus I'm an engineer/physicist so I know what it takes to protect a package. So I never have shipping damage...well almost. I did have a component of an amp inside the amp become dislodged during shipping and I worked with the buyer to get that fixed.
If a seller doesn't agree to ship on their nickel and take responsiblity, then pass. there are other peices of equipment out there. If they seem uncertain about their shipping abilities, I pass.
Jerry