The eIS is a Seller Protection program designed to encourage US sellers to ship internationally.
Almost all parts of the Money Back Guarantee become inoperative when the seller uses the eIS.
The seller only has to deliver to the eIS hub in Illinois - after that Item Not Received claims are handled by the eIS and the seller is not responsible.
The eIS usually handles import fees, and the buyer pay them upfront. This stops the 'customs delay' scam.
The seller is still responsible for Not As Described disputes, but only has to provide return shipping from the eIS plant. Otherwise the buyer is responsible for return shipping if they want a refund.
There is very little in the program for the buyer.