I watched Madbid for a while and while i noticed the same winners coming upon several occaisions,it seems to be genuine, what you have to realise is that bids cost £1+ each so where they are selling something for £7.00,they are actually already raking in £700+ in bids, plus the price of the item.
I think you just have to watch and bid sensibly, I tried to work out when things were going for bargain prices but there seems to be no pattern, just luck.