Groupon deal an oven cleaner did:
No daily deal critics are perhaps more outspoken than Peter Shankman, a New York-based investor in several successful internet companies and an expert in marketing strategy.
"Groupon scares the living hell out of me," he told BBC News.
"How do you sustain a model where on average the customer, not the person who buys the coupon but the business itself, loses money?
"You get companies that don't know any better, they lose 10 grand, and they don't come back."
Among business owners, this is a common concern.
Massive, loss-making deals have been part of marketing strategies for many a year - but always with the underlying hope that once a customer is "in", they may stick around and buy something else or, at the very least, come back again another time.
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I'm happy with the results. This is something to get people in the door.”
Art Harris Owner, Pizz'A Chicago
There is also the chance to upsell - that is, offer extra services on top of the voucherspecific deal to turn a loss-making offer into a positive one.
But for business owners like London-based Hannah Jackson-Matombe, this just simply isn't happening.
"It's been a disaster for us. We will never do a Groupon deal again," she told BBC News.
"They're dangling a carrot that's practically irresistible if you're a new business and you're desperate to get out there."
Her company, Spotless Organic, offered an oven cleaning service for £19, down from its usual price of £99. Three hundred people purchased a coupon, of which so far around 150 have taken up the offer.
Under its terms, Groupon (like most other deal sites) keeps the revenue from unclaimed vouchers unless the buyer requests a refund.
A screenshot of an offer on Groupon Some of the discounts are staggering
Of the ones that do get claimed, the money made is split 50-50 between Groupon and the business.
"Their approach is to get you excited about the coverage," Ms Jackson-Matombe said.
"They say they're going to get you 300 more customers. You're going to be able to upsell your business. But if you're suddenly inundated, you have no chance to upsell anything.
"You basically work for Groupon, delivering something that only they benefit from."
She estimated that, on average, she lost £35 on each of the 150 or so oven scrubs performed so far - with next to no return custom.
"We've had very good feedback from customers on the whole. But if you're paid £20 for a service that would normally cost £99, you wouldn't do it - I wouldn't do it!"
