I've got to buy four tickets for an upcoming trip, and I'm tempted to save a bit by buying one of the airline vouchers for sale on eBay. The vouchers are the ones with a certain cash value (instead of "free companion flight" or something else like that). For example, these vouchers were issued when someone got bumped or when someone received some money back when price dropped. The vouchers are said to be transferable, but I assume that the terms also say they cannot be sold (though of course no one mentions that in the eBay listings). I recall awhile back reading about airlines monitoring eBay for sale of FF mile awards. Is it truly risky for me to buy one of these credit vouchers? Has anyone here purchased them and used them with success? Anyone used them and later one got their $ amount invalidated?