How do they choose the pairings?

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I have been watching the show for a while, and I was wondering how they come up with the pairings for the 'pod'. I was watching the couple who made heaps of money, Steve & ??. (One male, one female). When I first saw them come on, I did not think they would do very well, but then after watching them for a while, I realised that they had quite a bit of knowledge on various subjects between them.