Karina, I offered a deep discount, 70%, using my advertising budget for that month rather than assuming I would make a profit from it.
To my surpise and delight, the vast majority of people purchased almost twice the voucher amount. I actually made a small profit during my feature.
However, the biggest benefit I've had from Heartsy is the exposure. I had 5 sales when my feature began, and 40 when it ended. I know have almost double that amount of sales (one away from 80 now!) and have only been on Etsy since Feb of this year. I'm still getting sales from people who saw my shop on Heartsy but missed the deal, as well as repeat customers from the ones who purchased.
The number of sales I received that day has given my buyers confidence, since we can't hide our number of sales. The feedback coming in is amazing which also helps people have confidence purchasing from me.
Like you, I can only price so high. I have increased my pricing since the feature. That was one lesson I learned from it, my pricing was low to make the profit I need.
But, like I said, I used my advertising budget for the month to "pay" for my feature, so regardless of the outcome, I wasn't going to lose any money.