I'm going to give the point of view of a seller. Let's just say as an example, that the seller uses their own boxes, not ones that are provided by the PO and their own package materials? Did all that just fall out of the sky for free? That cost does not show up on the shipping cost from the PO. Now if I have to use shipping supplies from the PO that aren't free, like the ones you have to buy because they don't have the right size, the minumum I have seen an average sized box is say $3.00. Plus they sell bubble wrap, which is about $4.00 for the smallest roll. Then tape, which is about $3.00. I also have to drive about 10 miles, round trip to the post office, so it is not in walking distance of me.
Usually, I put a flat rate shipping with sig confirm and insurance and sometimes I have to take money out of my pocket to cover the shipping costs. I don't email the buyer and say "Hey can you send me the extra costs to cover because I underestimated". That would be tacky.
Also, I have bought things from stores where I thought the shipping was ridiculous, say from NM and I bought a Chanel nail polish and the shipping was $8!
I know some buyers also get upset if you don't send a thank you note with the item. I know this because the one time I didn't send a thank you note, the person got upset. It is a transaction, not a baby shower. I don't think things should be gift wrapped unless it is in the auction specifics. I do think things should be wrapped so that the item does not get damaged.
At this point with ebay, I am just happy when I bid on things and they are as described and authentic.