Groupon is waaay over valued. They have until recently been giving tons of stuff away. For example, everyone who signed up for emails telling them about new deals in their area would receive a $10 or $20 Groupon cash gift to use. This was widely exploited by people who frequent "cheating sites". These free codes were also able to be stacked on accounts. People have used this method to get everything from free dinners to free lasik eye surgery. All anyone had to do was keep creating Groupon accts...and repeat.
Im am 100% positive that Groupon has been exploited for tens of thousands...maybe millions.