Hmmm, I've never seen anywhere that I'm aware that states you have to charge what the postage physically costs, there is materials, and time to pack as well, they all have a cost, and that cost should be taken into account in the postage costs. I don't sell much, just mainly old stuff that's no longer required, mostly with free delivery (which of course is built into the price). My biggest problem is actually getting around to listing it.
Actually having just Googled this I came across a
page on MSE, which states user can't increase postage costs to cover fee's, but I've often charged more that the physical cost and I've used the Ebay postage system to buy and print the labels and have never been challenged, but then I do only charge reasonable prices.
If there is another easy way to sell something, such as forum classifieds then I'll use that instead, but other wise I use eBay. If it's left sitting in a cupboard then I get nothing, at least selling on eBay I get something back. In one recent sale I sold £150 worth of wheels/tyres for a £1 maximum fee, and the guy paid cash so no Paypal fee's
