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@jofijohnjoseph wrote:

in cases where couples file separately, both spouses must itemize their deductions, or both spouses must take the Standard Deduction.

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The part you continue to get wrong is that no one is forced to take a standard deduction, only effectively barred from a standard deduction if the other spouse itemizes.  Getting back to Bob's point before you snapped at him for trying to help you, if your client wants to itemize, nothing is stopping you from itemizing and you can stop caring about anything else.

It sounds like you have inquired enough to at least have a reasonable guess that the spouse is not itemizing.  I would document why I believe that to be the case (asked these questions, got these answers, reviewed prior year returns, etc.) and take a full standard deduction if that is more beneficial.  If, instead, you believe the spouse will itemize, I would take IRonMaN's conservative approach and itemize.  It is the client's tax return so the decision starts with them but you're also signing under penalty of perjury to do what's best for the client . . . or however it's worded on the tax return.  So IMO you need to be comfortable with the position taken on the tax return before filing it.

Rick