let me start by quoting another user since i had the EXACT SAME PROBLEM
'I travel across town because I bought a Groupon for this place. It was a $20 Groupon and they wouldn't credit me with the entire amount. They said they had to take out the tax... Huh? There was additional tax added to the receipt! They said that's how they do it... What?
I talked to Groupon after, and they said, No, that's not how it's done, so don't fall for it!'
pizza was ok, nothing great. the server was attentive and nice but pretty clueless (had to explain what i meant by needing a garlic shaker...at a pizza place(?) told us wrong specials of the day, etc) the real problem was the bartender/ cashier who is the first person i've dealt with who told me 'oh we don't give the full face value on groupons'. took ten minutes of arguing and her changing her totally illogical excuses multiple times. finally accepted it and acted like she was doing us a special favor. avoid.