Are these exclusively for flights in the coming 7 days? And does winning actually purchase a ticket (thereby guaranteeing a seat)?

Because if the whole excercise is to simply make money on a seat that would've otherwise flown empty, take the marginal cost of an additional passenger, add a little bit, and start the bidding there. If it's not guaranteed anyways OR there's a strong enough assumption that if no one bids on the seat then it'll anyways fly empty, why start so high and lose out on potential customers? Not like people who actually want/need to fly will stop buying tickets because they might be able to bid on tickets at the last minute