So the UI allows users to set a discount rate, similar to the way you set a limit order on etrade or Name Your Price on Priceline. I can place an order to buy AAPL for $100 or bid to stay in a 5 star hotel for $10. Doesn't mean they will get filled.
I do agree, though, that those very high discounts should be a red flag, if they're for any serious money. Stuff for $5 with a 50% discount is no big deal if someone just wants ot be rid of a card and doesn't mind losing a couple bux, which they'd end up paying in fees buying BTC anyway.