I can only speak as I find, and I have found that on other places where I sell cards, my sales have increased since I stopped charging for p&p . . . .The price you see is the price you pay . . . .this has gone down well with my buyers and I'm noit out of pocket by doing so.
I find it off putting when I see something I like going for a reasonable price only to find when I add the p&p it costs a whole lot more. And sometimes its cheaper to buy it in a high street shop and go get it myself !!!