Just as Yipit, DealRadar, and DailyFlock have emerged as clearing houses for group-buy deals from Groupon, LivingSocial et al, the group-buy phenomenon has given rise to another new business opportunity – marketplaces for buying and selling purchased-but-unused group-buy vouchers.

New marketplace sites such as CoupRecoup, Lifesta, and DealsGoRound allow people to post their hastily purchased gym sessions, beauty and spa treatments, VIP club passes, restaurant reservations etc, name their price, and sell them on (recent TechCrunch and WiseBread commentary).

It’ll be interesting to see if and how these new social commerce sites, pitched as Craigslists for Group-Buy deals, manage fraud (why not use the e-mail voucher AND sell it, by simply printing it off twice?) or the professional eBayers’ trick of snapping up popular concert tickets in bulk and selling them on at a profit (UPDATE – see how lifesta are managing these issues in comments below).

But we think this addition to the flourishing group-buy ecology is smart – aggregation is the future – but we also think it’d be better if Yipit picked up the phone to CoupRecoup, Lifesta or DealsGoRound and combined forces to offer a one-stop shop for buying and selling new and previously purchased group-buy vouchers.

And for brands still on the sidelines of the group-buy social commerce phenomenon, deciding whether it makes sense to use it as a product seeding and word of mouth vehicle for launching new products, we think this emerging ecology of group-buy related sites is testimony to a popular and healthy trend.