Hi EP....I used to enjoy selling from 2001 to 2008, and I came across all kinds during that time....thankfully only a few over all those years caused me any real grief. In fact, more sellers have ripped me off than there have been annoying buyers...so I guess it goes both ways....
I think I'd be a bit annoyed by all this too....Ebay have given buyers so much power, their expectations are becoming unreasonable. Unfortunately with the removal of two way feedback, the balance of power has swung to the extreme and sellers either like it or lump it. All you can do is avoid buyers who want to make unreasonable demands.
Postage however, has to be the single biggest bug bear of all buyers...and it's something that Sellers need to pay attention to. When I was selling, I was happy to combine for cost, because buyers will purchase more if you keep postage reasonable. I didn't charge for packing because it's everywhere begging to be recycled. I didn't charge for handling, and when I had to buy packing material, I purchased a 50 mtr roll of bubble wrap regularly for 25,00, working out to 50 cents per mtre...too easy and something that isn't noticeable when it's built into the purchase price.
But I was a collector/seller, not a business. Not saying your postage was too high, just saying it's something I email sellers about predominantly, and which causes many of the disputes on ebay. Some sellers do little to keep postage costs as low as possible, and many don't realise they are doing it....
e.g. I just purchased three items from a seller, who was absolutely fantastic to deal with.....fantastic....they are obviously an ex powerseller, who has now opened their own specialty shop and website in an effort to move away from Ebay...who can blame any serious business...it's the only marketplace where the business has absolutely no rights and no recourse. I was able to view all the same products on their website, and the prices were the same....too easy...oh and they have a merchant facility...yippee !!!
Anyway.....the only mistake this seller made, was to send the items in a massive tough bag, which ultimately cost me about 4.30 extra . The items could have been sent in a prepaid satchel for under 10.00, but I ended up paying 17.00 or more to have it sent from qld registered....So in my view, the seller didn't pack the item cost effectively.
On my next purchase I will as a prerequisite, ask that seller to send the items in a prepaid satchel...I'm sure the seller wouldn't be offended because it means I'll become a return customer to their actual website.
Some sellers do take offense if a buyer questions postage, so again, it goes both ways.
Being a buyer and seller, I have empathy for both parties....if only Ebay would stop interfering with the buyer seller relationship as their UA states? Restore two way feedback at least.