I recognise that some religious traditions take guidance from more than just the official holy books, but even the official Catholic view seems fairly neutral: that gambling is not immoral in itself, as long as certain conditions are met:
The fact that Swoopo promotes itself as an auction/shopping site and lists "strategy" as part of the experience skates uncomfortably close to the "no fraud" clause listed in that link, although offering discounts to losing bidders would seem to give them a solid "it's only gambling if you choose to treat it that way" out.
It's not anything like widespread enough that you could say it was a "Christian teaching," though. While you can still find people who say it's sinful (and you will always be able to), it's getting so that standard Southern Baptist Sunday School materials say, "Is Gambling a Sin? Well . . . not reeeeeaaallly . . . but we don't think it's a good idea." And I think those guys are usually just about the last to let go of issues like that.
Gambling is considered a form a stealing since the person who lost doesn't actually want to give their money to you, they are forced to by the roll of the dice. In normal commerce you get something when you pay. (And don't say people enjoy playing, no one enjoys playing, people enjoy winning.) I believe, but am not sure, that lotteries are not considered as bad though.