6. If the flight is oversold they offer $700 travel credit. I almost got one (I had a United award flight as backup). I can't imagine how long it would take to use up $700 buying cheap fares, although I presume that airport counter purchase would not be an option.
I would not recommend taking one of these voucher offers unless you really know what you are doing. They come with more fine print and strings than you can shake a stick at. E.g. F9 vouchers are usually only good for a single use and only cover the base fare (not fees or taxes).