Here’s a well written article on Heartsy and whether such deals paid off.
Don’t just read the article. The comments are pretty numerous and from sellers that have used Heartsy as well. An interesting read.
Personally, I do think the advertising will pay off, even should the seller incur a small loss to begin with. Afterall, the cheaper deals will enable many to purchase in larger amounts and advertising will also spread through more blog entries and word-of-mouth/ or when the items are gifted.