It's not difficult for a seller to end a listing, it's easy for a buyer to retract a bid and it's easy for a seller to cancel a bid, as long as you're not in the last 12hrs of the listing. Buyers can select "Bid the wrong amount" as the reason for retracting a bid, so bailing on any auction is easy. Sellers can select "Bidder is from a country I don't ship to" or "Unable to determine identity of bidder" as the reason for cancelling a bid. There is no "Bidder has insufficient feedback" reason, so if that's the reason, the seller just has to pick something else.

It's fairly easy to setup listings to automatically reject bids from countries you don't want to ship to, and many int'l bidders have US-based drop boxes as valid shipping addresses.

2nd Chance Offers are a weird, mixed bag. As a seller I seldom send them, since they almost never work. When I do send them, if the 2nd-place bidder doesn't buy within 12hrs or so I usually just relist. As a buyer I rarely accept them, especially if there's a significant gap between me and the 3rd-place bidder. Rationally I know I'm getting the item for what I agreed to pay, but it doesn't feel fair that the seller is getting my highest bid just because the bozo winning bidder backed out. And if the seller is shill bidding, I'm rewarding the practice. Like CliffordK, I've offered to buy 2nd Chance items at the 3rd-place price plus the bid increment, but that's never worked.