When you make a second chance offer, (I noticed for myself, anyhow) that they 99.9% of the time don't take it - even if you have one of those situations where your auction ends at 6:01, winner messages you at 6:02 they hit an extra 0 on their keyboard, you check the bid history, and the next bidder bid at 5:59. You send the SCO and *poof* nothing.
So, lately when I send a SCO, I message the buyer directly (you know you can't message a second bidder, the system circumvents it) right after sending it, saying they just got a SCO from me, and its a great price, etc, etc. That one message has increased my rate of SCO acceptance. Just saying, its a 2 minute thing thats worth a shot.