If it was that important to them, they should increase the offer until someone is willing to take it. I guarantee people on the plane have a price at which they'll agree to take the next flight. But yeah, asking nicely does help too.
Yeah those vouchers sound shitty as hell. Terms and conditions may apply.
Basically monopoly money, $800 in monopoly money, they want to be able to say they offered $800, dollar-sign-eight-zero-zero, they want to put that in their response to why they were right and the passenger was wrong. But I wouldn't eg buy 800 dollars worth of travel vouchers in order to use those travel vouchers to buy a ticket.
