I've worked with Summa Solutions on a few occasions, http://summasolutions.net they do good magento dev. I'd be wary of random devs on sites like oDesk, magento can be a beast. if you're doing straight eCommerce, you're ok. If you're adding clever twists, the devs need to know how to bend magento in the right ways. I've personally fiixed many a botched magento codebase (both on shore and off). It can take as much as three times as long to undo some bad decisions as it took to put them in first place. If you decide on on-shore hit us up, http://arroyolabs.com