I'm a buyer, and I empathize with you. I also wont buy from sellers who charge too much for postage, unless the item is at a real bargain price. I've actually got into some quite unpleasant conversations with sellers about this when I have pointed out that their item can be sent for a much lower cost. I sell on another account, so I have experience with postage costs.

As someone else mentioned, some sellers might not realize they are being charged a fvf on postage too, it wasn't always like that and sellers could get out of high fvf by pricing the item low and postage high.

Because I also sell, I can see it from the other side too. Once ebay and paypal have taken their cut, you have paid a promotion fee (if you use one) you have bought a box or satchel, bought or found some kind of wrapping, gott everything sealed up securely and addressed properly, bought more printer ink, waited in the post office for 15 minutes, got stuck in traffic, spent almost an hour making the listing in the first place, fought with ebay glitches and realize you are only going to end up with $10 for all of that, it seems justified to add a bit onto postage.... or somewhere.

Or It can be difficult to know exactly how much something is going to cost to post, if you are not used to posting stuff. 

I usually add between 50c - $1. (for packaging) and I try and price my items to cover everything else.

If you buy from the US or UK you are paying extremely overpriced shipping via the GSP, that makes our postage costs overpriced by a few dollars look like a bargain. I get more annoyed at paying the exorbitant GSP fees to Pitney Bowes than to local sellers who add a bit more on to cover fees and time etc.

Sometimes a seller will admit that their postage is overpriced because they are not sure how much it's actually going to cost and they want to cover themselves, they will sometimes agree to refund the exess after the item has been posted.