This may have been asked before but I can't find an answer to it anywhere and it still baffles me. In the 7th book how is Ron able to tell Harry that Bill and Fleur live at Shell Cottage?! Bill tells Harry he is secret keeper therefore only he should be able to tell Harry the location of Shell Cottage right? Or did I miss something?

From what I can gather, it is because as Secret Keeper Bill told Ron where it was because Ron stayed with Bill and Fleur after he left Harry and Hermione. From what Jo explains in Deathly Hallows, when a Secret Keeper tells another about a place the secret is passed on to them, so they can also reveal the secret. It does contradict what has been said about Secret Keeper's previously, though, and is a bit of a grey area.

I agree with you, because Peter was able to tell voldemort where James and LIly were.

I think it's also possible that Shell Cottage had Bill as Secret Keeper in between Harry & co. arriving and Lupin arriving. He might've realised that it's a possibility that he could be tracked there because the Trio just randomly showed up like that so he subsequently decided to do the Fidelis Charm. I don't think Ron could've told Harry the location if Bill was Secret Keeper at that point. If you remember back to Grimmauld Place in book five, those who accompanied Harry to Number 12 knew the location, but it took a paper written by Dumbledore (the Secret Keeper) in order for Harry to see it and enter. Pettigrew was the Potter's Secret Keeper, so he was able to directly tell Voldemort their whereabouts.

Actually, in the Deathly Hallows I think it was, Jo explains that because Dumbledore was the Secret Keeper for 12 Grimmauld Place and died, all the people he'd told automatically became the shared Secret Keeper. But that was because he died.

Bill was Secret Keeper and yeah he told Ron, and I'm hazarding a guess here, but maybe because Shell Cottage isn't an actual address, they could go there. Or because Harry disapparated thinking of Bill and Fleur's. And then Bill came out to greet them, and that's when Harry saw the place, once Bill met him outside.

Plus, I think it was the third book that said Voldemort could have his nose pressed against the Potter's living room window, and still not find it. So they can know where it is, they just can't access it.

Snape claimed he could not tell the where-abouts of the Headquarters, but he was good, wasn't he? And he may have said, because Death Eaters watched the place, but couldn't access it. I can kinda see a flaw in this logic, but it must be hard to write it all.

Sorry if that didn't make too much sense, I tried my best, and that's the impression I got. Basically, they can be told where it is, but not access the place if not told by the Secret Keeper. That's what I think, you don't have to have that view though

I like that theory, Zoerawrr. It's actually a very well-thought-out and reasonable theory to work with. And it goes along with Rowling's depiction of Secret Keepers. And that's all I have to add right now. I just lost my train of thought, so when I get it back, I'll edit this post.

Yeah I noticed that too. I think another possible explination could be that Bill gave Ron permission to tell Harry and Hermione about Shell Cottage in case they were in desperate trouble and needed to get there. (Which happened to be the case)

I agree with Zoerawrr, I think when Bill came out for them, it became visible.