Sad to say but the postage cost increase from the post office now means that I have to charge for postage whereas it used to be free.  Paperbacks will be sent letter class where possible and larger books will be sent small parcel class.  If a book weighs over 2KG the cost of postage is insane with the post office so I have started using UPS where possible.  Buyers from overseas should use the eBay postage service.  If postage costs are similar between first class and second class I tend to choose first class especially for smaller books where the difference is minimal.