This is always likely to happen when guesses and couriers are used.
If buyer lives in certain parts of the Country their delivery costs are much higher. Only Royal Mail delivers to all parts of the UK for the same price.
Never heard of the £1.30 fee, but will believe anything when it comes to making a profit.
As far as buyer is concerned the book was post free, and you were using Royal Mail, so you would have been in a position to check if ebay suggested postage was accurate. £2 would only cover a large letter up to 250 gms. with no tracking.