1) Signing on bonus. That 75,000 miles extra reward miles is a "one-off" for spending a certain amount at the start of the card. There is a cost of customer acquisition (CCA) for a credit card member and presumably some of the CCA is factored into the bonus. The 'hack' is to constantly apply, use, bin and then reapply for cards to maximize the bonus.
2) $1000 in airline fare isn't actually a $1000 liability to the airline, because that is the market price where as to them the cost price is going to be less... and as you suggest if they restrict it to a few seats per plane the cost price is even less.
2) $1000 in airline fare isn't actually a $1000 liability to the airline, because that is the market price where as to them the cost price is going to be less... and as you suggest if they restrict it to a few seats per plane the cost price is even less.