After winning an item, I often ask sellers to clarify costs if their rates are too high. It's amazing how many of them suddenly find that "the postage costs weren't as high as I thought they were now that I've checked. What I'll do is charge $xx instead."
After winning an item the spectre of negative feedback looms large for sellers and I think many back down on postage costs when they know that they're deliberately overcharging.
However, where someone states that postage will be something stupid like $29, then I always approach the seller nicely and ask them to clarify why the cost is so high, and if there are other options. If the seller doesn't want to discuss the matter then, well, you know they're looking to rip you off plain and simple.
Edited by Russell Gilbert, 07 February 2012 - 06:02 PM.