I haven't had a chance to read through all replays so apologies if I'm going over covered ground.
I ran some deals when I had my salon, they were great for filling the book up and made the salon look busy but such hard work for not a lot of money. I did retain some clients but in all honesty most were just after the best deal. I got tired of haggling with customers that wanted to exchange for something else and had so many not show for their appointment with no call or email and then expect to be able to rebook "because they had already paid"
I never worked with groupon, their commission was too high and when they did offer to run a deal I found a weeny but in the small print that stated once I had signed I would not be permitted to work with any other voucher site!
My advice if you were to run a deal would be:
1) Read all small print very carefully
2) Be very clear on your offer ie for what treatment it is valid and state a 48hr cancellation notice required otherwise voucher invalid
3) Haggle your commission, I had KGB down to 25% as a set commission and even 20% at times
4) Consider making your voucher only valid for your quieter times, it's saves turning away full paying customers and regulars and helps fill slots
5) Always give 110% in your voucher treatments as much of a slog as it seems, after all this is your reputation and you do want this client to return. You chose to run the deal and luckily they bought it
Chose your voucher company very cafe fully too, you will be associating your business with theirs so make sure that their reputation is tip top.
Good luck!
Hayley