well mate sometimes thats all it can take is a change of loft to put them off ,sometimes a change of loft will put a spark into them , but who's decision was it to wait for five rounds , the buyer or the seller,i know if it was me i would try as many rounds as i could just to see , like trimming his under feathers and his tail, same with the hen , then maybe try effamol tablets you name i would try different things then if he still didnt fertilise an egg, i would contact the seller for possible refund or swap for another equally well bred bird. You cant blame the seller for a bird not fertilising an egg ,even if he said before hand it was fertile .