Re:training, 100% correct. Always try and end on a positive note. If Diamond refuses a trick or command, end with one you know he will do, so you can walk away saying good boy, good bird. Try and train same time every day. BE CONSISTANT , same commands, same approaches, and lavish praise on him if he does a command succesfully and importantly reward with the treat IMMEDIATELY when he gets it correctly, so Diamond knows why he is getting the treat.