That is confusing as hell, rather than saying "you get 4 pounds off RRP, but you have to pay 2 pounds to the charity (which i'll pay on your behalf) and X amount for paypal fees' why not just have fixed prices and say "2 pounds from this purchase will goto charity". Because when you add it all up the buyer is only actually saving 75p, you're tell someone they're saving 4 pounds when it's actually less than a quarter of that you're just gonna get peoples hopes up. Besides, most of the time you don't get fee'ed with paypal anymore since they changed all that, it would be easier to make the buyer pay the fees (if any) which is also available now, that way you don't have to worry about the buyers who'll have to pay fees and the buyers who won't as it'll be down to them to pay them if they have to.