Here is a guide I found that explains how to exploit Bottle Caps in Sun and Moon. I highly recommend this exploit if you planning on playing competitively in game. https://www.reddit.com/r/PokeMoonSun/comments/5f9x25/how_to_get_bottle_caps_guaranteed_for_the_price/
I can confirm this works. I found someone after a wonder trade last night with this option. I actually already had that shop as well so I wonder if I've ever been that conduit for someone else. Curiously I get "registration failed" when attempting to add them to my VIP, but that may be due to some setting this random Japanese person happens to have set in their profile. So for now I'm just avoiding WTs and the GTS (which is fine, I have all of the non-UB version exclusives already) to keep them there. I figure it's best to make use of this now because I would not be totally surprised if Nintendo catches on and patches this in the future. I dislike hacking and typically don't use exploits when it comes to Pokémon, but I really don't mind taking advantage of this one at all due to a] the rarity of Bottle Caps and b] their use with IVs, which is one of the things people do actual hacking for in the first place (which I don't personally care for).
Understandable however I just want to mention that Hacking and Exploits are two different things. Hacking involves use of 3rd party devices that let you achieve goals in games that aren't normally allowed or possible. An Exploit is something available in the game and even if it was not intentional it is something legal to do in the game and to take advantage of. It is not bad to take advantage of exploits unless they are game breaking, like if there was an exploit where it gives me an edge or a game advantage then that's a different story entirely. Again just wanted to state that there is nothing terrible about taking advantage of this bottle cap exploit.
Yes you're right and it's a good point for people to know, and I agree. Big part of why I'm cool with this and like it. I'm glad you made the thread because I am not a Redditor and probably wouldn't have come to know otherwise. This is a great thing for how much of a pain Bottle Caps are otherwise.