I have tin whistle here beside me and I brought it to Scotland from Ireland where Im from and that was 7 years ago now with quite a lot of marks and dents. this I know is not ideal but it still plays the tunes but to a trained ear it probally sound like a cat getting strangled! luckily i dont have a trained ear so it doesnt matter to me!
Enjoy the web there is so much info on whistles that I m just finding now and loads of good tunes to try and learn also.