How long has this shoer been shoeing your horse? When and how did you notice a problem? I think you would do the most good by simply educating the guy by sending him the vets letter, X-rays, etc. With all the information on the Internet these days, seems like owners need to take a more proactive role in the care of their horses' feet. It is nice to think your farrier for sure knows what he is doing, but it is better to educate yourself and pay close attention to what he/she is doing. Have a farrier who is willing to communicate and work with you. No point in trying to get your money back...pick your battles wisely!