Rather than link to a competing forum here is a copy and paste from part of my post about Living Social deals:
Let's do some math. Let's say you manage to sell 250 deals for $50 profit each. ($200 regular price @ 50% discount to customer minus 25% to Living Social.) 50 of them never cash in, so 200 details @ 5 hours each.
250 x $50= $12,500
200 details x 5 hours= 1000 hours
$12,500/1000 hours= $12.50/hour minus expenses.
1000 hours / 40 hours per week = 25 weeks (6 months and you are stuck honoring the deals.)
Compare to:
50 full price details @ $200
50 x $200= $10,000
50 details x 5 hours= 250 hours
$10,000/250 hours= $40/hour minus expenses.
250 hours / 40 hours per week = 6.25 weeks
And now you have 4+ months to try to gather more business or do whatever else. If you are really desperate you could offer a free detail to someone if they send you two friends. You still come out way ahead and you can stop anytime you want.
It should also be noted that people have friends primarily in their similar income range. Those who can afford a full price detail have many friends who also can afford it. People who only can afford a detail because of the Living Social deal have a lot of friends who can't afford the full price either.
That's not to say it hasn't been done successfully. But that is only when it is a volume shop that can spare the manpower and have it not prevent work being done for full paying customers.