Tin doesn't rust. I believe what you are seeing is rust on the underlying steelw here the tin coating is scratched....or the "tin cans" are not tin at all but steel. Oxalix acid will remove rust. andw axw ill prevent it from happening.

im not quite sure, tho they weren't scratched at all, their surface was ok. all the pins i have rust pretty frequently and there seems to be 2 main kinds of material depending on the pin so i cant say for sure (first pic is the one that dulled, evidently and the second is another one i tried it on, where the rust left but the spot remained. they appear to be different materials though)