You do have to be careful with upping your postage costs to cover some of the ebay fee's. Someone did that with us and we complained as I didn't think it right (and knew damn well it was against the rules) for the seller to expect us to pay her ebay fee's through 'postage costs' even though we were collecting the item lol. We ended up not buying the item at all as all trust was lost. As a seller, usually, I am careful to charge as minimally as possible for postage fees.
As a seller, I'm afraid, you have to accept that ebay fees will be incurred. Think also about the costs of running a shop.., far far more than ebay fee's. My fees run at about 10% or less and to be honest, I have sold mobile phones in quite large quantitities recently and found the fee's to be a lot less than 10%. I don't think ebay fees are that unreasonable.., it DID allow me to appeal to a very wide audience (I have quite a few regular European buyers now) which i would not find it as easy to get without ebay.
Yes, there have been a couple of times I've been burned through the rules on ebay, both as a buyer and a seller but I know this happens and its just one of those risks you have to accept.