That is exactly how I feel about it. The shipping charges are clearly stated, so if you don't agree with them and are going to ask for a refund, then don't bid--or if you really want the item, see if you can work out a lower shipping rate ahead of time (NOT after you buy the thing) with the seller.
Sellers arrive shipping & handling fees based on all sorts of things, not just the actual shipping costs. Bubble wrap is expensive. Paper is expensive. So is tape. So is gasoline. The seller's time isn't free either.
Next time you are tempted to ask for your three or five bucks back "on principle", just think about the reasons why a seller might have set that shipping fee the way they did (and think about the fact that you as the buyer agreed to it!).
This is in NO way intended to bash buyers, because obviously as a seller, we need you!! But I just wanted to take a second and give you some food for thought about what else might go into the shipping & handling of your item.
edited because I wanted to add that if you pay for Priority and get First Class--that's totally different!! I would absolutely ask for (um, demand) a refund in that case.
I also won't bid if I think the s/h is way too high. I don't mind if they are making profit, which I never really think they are doing. Yes, there are those that do that, but I stay away from their auction. I also don't live next to a postal office. Sometimes it takes me over an hour. Like others have said, factor in the sellers time, the supplies, boxes, paper, gas, and well of course the actual postage.