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Well, if you have a good working checker, what's the problem? Are you simply not getting hits at all, or are getting 2FA protected accounts?
Cracking Nintendo accounts is a consuming work. You will definitely need to buy some very high quality proxies. If you're using free combolist, I'll recommend buying private combolist from a reliable seller.
For Nintendo, yes you will need a capthcha service, which will further bring your costs up.
Dm me @Rosenberg64 to tell what problems you are facing.