>In practice, a lot of grouponeers are just trying to save a few dollars and won't be back nor tell their friends.
That's because of shit like >>12074
When they provide decent service despite knowing I'm using a voucher I become a repeat customer at that establishment and tell my friends (if they're any good anyways).
Pretty much any of the ones that aren't chain restaurants require you to declare your voucher before being seated. Some actually require you to call ahead if you're using a groupon voucher (no doubt to pull ou the older shit they can from the freezer to prep it). There's a Vietnamese place that's always on the groupon/always skimps on the food for said grouponers here in town who lost their shit when someone didn't call ahead to tell them they had a voucher/were going to turn them away before realizing my ma' and I were the only other people in their shitty restaurant and we were about to get up before our food was even served while she was complaining to her cook from what she thought was a quiet corner.
Honestly I try to avoid groupon after I bought a $50 one for CCW training courses and found out it didn't cover using a gun or ammo, or the range time, or really anything other than the physical class itself which was held off-location at some church.