I've know at least two people who've been caught out by this so it's probably worth mentioning it here.
If you have an Amazon wishlist then the URL you see when you're logged into Amazon is no good for directing other people to it: they will see either their own wishlist or a page inviting them to create one, if they're not logged in to Amazon.
This is easy to be caught out by: you put the link somewhere, test it by following it, and find that you do indeed get your own wishlist. Unfortunately it won't work properly for anyone else.
To actually find a usable URL for it you have to log out of Amazon (or at least use a browser not logged in to Amazon, in whatever way is convenient for you); find your wishlist in that; and use the resulting URL.