Let’s say you used one of those sites that offer dining discounts to buy a gift certificate you no longer want. Don’t fret! A new site, Lifesta, lets you sell your voucher to someone who didn’t read about the restaurant’s rat problem on Yelp. “It’s a marketplace,” says co-founder Eran Davidov, noting that sellers often offer the deals at the same price they paid for them, or just slightly higher to account for the site’s 99 cent transaction fee and 8 percent commission. “People will buy or not.” But is this kind of thing kosher? Or is it on the same questionable ground as reservation scalping?