You obviously didn't bother reading the link. Both parties add collateral ideally equal to the item price: so the buyer pays 2x the price and the seller pays the list price and sends the item. If the buyer is happy they've received the right item without issue both click a button to release their collateral back to themselves and the buyer's money to the seller. If not they have to agree how much to release to each other since they both have skin in the game.
So in your example you can sell an ice cream for £10. When I buy it for that I pay £20 and you pay £10 and send the item. I eat it and we're both £20 down. So I want my £10 back and click a button. It then releases £20 back to you - the item price and your collateral, and my £10 collateral back to me.
I did read it but you are right my comment doesn't reflect it.
I always thought that this part of a smart contract is ridiculous as it binds the same amount of capital as the transaction is worth on both sides.
It also doesn't fix the issue if someone with much more money than you wants to f** you over.
It also does assume you would find a good solution together just because of the capital invested but you know there are plenty of people who are not able to negotiate proper.
It just doesn't solve the issue and it doesn't solve issues like if the shipment is lost on sea. Or it's getting stolen.
A independent 3th party actually helps solving those issues.
Nothing is perfect but I think in the majority of cases it'll work as well as a trustable third party but without requiring one. If someone with much more money wants to screw people over at least they'll be paying a non-nominal amount. For bigger items that kind of attack would get expensive quickly.
The amount of collateral is configurable by sellers, and since buyers will soon be able to message sellers that means it's negotiable.
So in your example you can sell an ice cream for £10. When I buy it for that I pay £20 and you pay £10 and send the item. I eat it and we're both £20 down. So I want my £10 back and click a button. It then releases £20 back to you - the item price and your collateral, and my £10 collateral back to me.