There is no third party guidance on how to decide whether an account is for business or household use. That's your bank's basic due diligence responsibility at account inception.
If the account title is:
"Sam Fouts or Laura Fouts" then as far as I'm concerned it's a consumer account for the purposes of Reg E, Reg DD, etc. They may run business receipts and expenditures through the account, but I'm comfortable with that classification because 1) the water isn't muddied with the name of a business and 2) that's the conclusion that best protects the consumers.
"Fouts Farms, LLC," then I'm comfortable saying the account was not opened for personal, family or household use regardless of the fact that they run non business expenses through the account.
"Sam Fouts or Laura Fouts dba Fouts Farms," but the account was not documented as a partnership, no EIN was obtained, and no dba certificate was obtained then you have some real holes in your account set ups. On this issue (and many others) the bank has just decided to flip a coin whenever an important choice needs to be made. You may default to classifying it as a consumer account for this purpose, but it does not resolve the more critical issues.
Yes, I was reared in an ag bank. "Sam & Laura" are my great grandparents.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.