Having said that, I also went for a great Groupon meal somewhere else, which included a cocktail that was so good I had another 2, bought more food on top and ended up paying as much as a 'regular' meal would have been elsewhere (and tipped accordingly for the good service). That was the exception to the rule, though, even based on a very small sample size.
Do many people leave 2½% (essentially no) tip in London?
It doesn't mean everyone using groupon is automatically a jerk, but it definitely selects in that direction.
Yeah, because absolutes like this help. Groupon customers can be just like any other customer out there. Some "regular" customers will get cheap wine, some will get an expensive bottle. Similarly, some Groupon customers will get the cheapest wine, others will take the money they saved by getting a Groupon and get the expensive wine. Being a "Groupon customer" might move the needle towards one direction but it's far from absolute the way you're making it out to be.