I won't know, how you could go for a whole paragraph in Caps without knowing you're doing so. You are all wrong about GSP, anyway! I explained it all.  🙂

If the Buyer refuses the package, then Seller has lost a sale. What good is that?!  Oh, Seller could have the item back! Okay, but Seller has lost time and opportunities. It's a total loss. By the way, a Return package loses insurance coverage if original insurance coverage is obtained from a third party. 

Note; in most of the cases, it's cost effective to buy insurance from third party, specially, in high value packages.

Sellers have an option not to get involved in Custom fees. Depending on value of the item, Custom fees is the most important part of a deal and almost all the times, appears as first question in Buyer Inquiries from U K. 

I wouldn't know if my Buyer in U K is a 'U K Citizen' or not, that's a very racist approach. I am sure, you meant; U K residents and all Package Receivers in U K, are liable for Custom Fees. Simply put; ' Receiver is liable for Custom Fees'. Anyway; 

All carriers charge for their Custom Fee collection and handling. Once they collect money for a service, they become legally liable.  They are the acting agents on behalf of Sender. Even if Receiver pays the Custom fees, a lawsuit could be initiated by Sender once a request is obtained from the Receiver on negligence of service provider. All overcharges are liability of the agent or service provider. 

Sure, you're absolutely right, Seller is the responsible party  for the Custom Fees. Sellers/Senders should get themselves familiar with Custom laws and fee collection before attempting to argue the merits.  That should be the golden rule of every business; if you don't know how to do it, don't attempt! 

I have given an example, unfortunately you've missed it. It's Message 12 of 27 😃

I know, too much going on here