One thing you forget is there are often people flying standby (people who work in the travel industry, and people who want to get home earlier, or people whose flights are late, or cancelled and get put on a different flight. They won't let a seat go empty if there is a body to fill it.

It's a dumb idea. Most tickets aren't refundable these days; let alone the ones that are need to be cancelled beforehand. Prepare to not get a refund.