Given Groupon's published payment terms, this article is a little odd: http://www.groupon.com/pages/merchant-terms-of-service-1 (see 4.3). It seems they're paying merchants only after coupons have been redeemed. So in reality, merchants get their cash later than for regular purchases. Of course these default payment terms can be overridden in a custom agreement, but I wonder how often this really happens?