First, have a lot of T-credits (and sufficient funds) handy. Some auctions drag out and can get expensive.
Second, be aggressive. Just don't be bloodthirsty, or else you'll use up your credits and have to eat the cost of getting more credits. The Pricebenders auctions can get rather addictive.
Third, just have fun. Simple as pie.
And that is how you win a Pricebenders auction. ;)