There is no such thing as a free lunch!
Groupon, like other group discount sites, are pushing businesses to feature money-loosing deals, taking 50% of what you pay from business and convincing business-owners that people once visited the business will continue to do so over and over again paying full price. Life shows the opposite.
If you bought an incredible deal from Groupon, you must know that the business, you about to visit, looses money on that deal. To recuperate, the business will use all kind of strategies - from up-selling at higher-than-usual prices to cheating or closing the doors on you. So, be prepared. If you think you are strong enough to not submit to sales pressure, you also must be prepared to receive low-quality service in return (you know, when business will realize you cannot be milked, they get rid of you by giving you $#*!ty service).
My advice is instead of buying coupons from Groupon, call the company they advertise and tell them you want the deal but like to pay directly. You will need to pay, may be 1 cent more, (in order for business not to violate Groupon agreement), but you're guaranteed a happier experience.