A photo is the property of the photographer the minute it is created. That also means the photographer holds the copyright. Photos posted on the Internet do not become public domain property. Christina may be "a great chick," but she used someone else's property to generate profit for herself, without asking permission or offering compensation. That's pure theft. The medium from which she obtained the photo is irrelevant. Saying that if you don't want photos stolen, don't "post them in the worlds [sic] largest market place [sic]," is the same as saying to a book author, "if you don't want your words stolen, don't publish a book." If Christina walked into your garage, took your lawnmower, sold it, and kept the profits without asking permission, you'd consider that theft. This is no different.
Should Flricordia have contacted her first? That argument could be made. However, as Flricordia pointed out, this involved two other entities. IMO, he chose the correct route and it is to eBay's credit that they enforced their own rules and acted promptly.
Gary