You can never really know.
You craft your world with care. You name your characters and locations, and usually you hear the sounds of the words in your head. Maybe you become highly attached to a name, as a particular character grows into it. You've given it a careful spelling, of course, to represent as closely as possible that perfect name that resonates in your head.
Then, say it gets published. Someone walks up to tell you how much they liked the character, and they get it wrong. Badly wrong, so wrong you can hardly recognize what they say.
I suggest that you appreciate the person greatly. After all, they went to the trouble of reading your story, telling you how great you are, and liking your character so much.
You don't have to imitate their pronunciation of the name, necessarily, but don't try to correct them. It's not their fault. English spelling wasn't designed to indicate spelling unequivocally, and fantasy names often use European or other foreign sound systems anyway.
Blame it on the limitations of orthography, not on the person. We don't write in IPA - and if we did, nobody could read it.
I won't blame you if it gives your gut a twinge to hear a name pronounced differently. When I wrote my first novel (still in revisions, because I've learned a lot since then), I created a character and named her Catin. Can you guess how I pronounced it? Well, I got together with friends and discovered they were rhyming the name with the word "satin." I went "aigh!" I asked them for help. I said, "How the heck can I spell this so it will sound like....?" We tried. Since then it's been spelled Catín - but fortunately I've also adopted a new attitude of curiosity rather than prescriptivism.
I'll be looking forward to hearing what you think it sounds like.