The couple of times I've complained about postage costs have been when the item I've bought has been so expensive and weighty that sending it insured would be the only sensible option, so I didn't really ponder it too much before bidding.
The last instance was a 3kg glass vase with a £175 pricetag and £23 for shipping. Special delivery for that item would run to a little over £20, so the shipping cost didn't really raise any alarms as I'm fully used to paying that kind of sum. Then it arrived with an £8 Standard Parcels label and I wasn't too chuffed. I don't mind paying for things posted well, but I do take exception to dealers like that.
But less than £3 difference I wouldn't really even register, never mind grumble over. Thankfully I've not had any buyers quite like that. Although I did have one buyer through my website (with free shipping, like yours) who bought a handful of items and then tried to demand a discount because the shipping was built into the cost and it would cost me less to ship them all together than if several people had bought them.

I guess there's no avoiding such folk.