For the most part I won't "pay" for shipping on ebay. So if I would bid $x then I actually bid $x - shipping cost. Unless I really want it. So shipping cost stops me from bidding on a lot of things.
This is what I do... I gauge what the shipping added on is, and if it puts it out of my reach of what I wanted to pay in the first place, I walk. I do this even with online retailers like Amazon or EE as well. If their shipping jacks it or I can't get free, I bail on the purchase... It's all consumer perceptions really, but it's enough to make me walk on many auctions on Ebay. You see something BIN for $10 you really wanted then the guy wants $12 shipping and you know you're getting it in the cheapest shipping method possible? It's a turn-off to the seller, but that's me.
I never sell stuff on Ebay... Looks like too much hassle. I buy, but even that I do less of than I used to.
The other day I was buying a model kit from Asia... Only way to get these kits, and they're awesome, but incredibly expensive. I went through a 100 listings easily before I settled on the cheapest one between shipping ($3? Asia? Wow.) + BIN price... I got it for less than $40 where these go for well more than that usually.
Likewise my RC tanks, I get many from Asia and they're huge. I have to see a shipping I can live with or it jacks the BIN so high... A friend of mine who sells and is in HK tells me how shipping isn't bad at all if you do it right, but many sellers overcharge because US customers assume it costs a ton to get something from them. It's all in the packaging and the shipping method, and of course tracking it so it gets from A to B for sure.