What it actually does, even to the salons who refuse to take part in the schemes, is suggest to the prospective client that there will always be a new offer somewhere else. Of course lots of clients will stick loyally to their chosen therapist, but for those who might want something extra they're encouraged to look at the offers. Hell, I've even had my most long standing loyal clients say they've had a spa day/pedicure/insert treatment here/ courtesy of Groupon etc because, well, how bad can it be for £25, when a Shellac Spa pedicure with me is over £40. True, they wouldn't go again because, well, it was ok for an offer, but I've lost out on that sale, haven't I?
And of course, the other place now has their details and will start marketing to them.
In my opinion it is a poisonous, myopic business model which will have made Groupon et al a lot of money, put some less astute business people out of business, and fostered an unsustainable, unreasonable expectation from the buying public.