The thing that really bugs me is people charging $20+ for USPS Parcel Post or UPS ground for an item that would easily go for $8 or less.
If I'm interested in the item, I'll let them know that and ask about the shipping. I usually get something along the lines of, "I have to get a box and spend time wrapping it. Then there's driving to the post office, that takes gas, and I have to pay postage."
So, I simply let them know that the Post Office provides free boxes which can be delivered to your door for free, and on top of that, you can pay online. After that, all you have to do is leave it at your mail box, and your carrier will pick it up on the next run. All this saves you time, money (save a few cents buying online, too), and gas! Yay!
99% of the time, if I get a response, they simply say, "Well, this is how I've been doing it, and I'm not changing."
People always want things free and easy. I show them how it can be that way, and they're too greedy making a few extra dollars off shipping to change.