Ask the guest how they would like to be addressed and address them according to their wishes.
I think the general modern rule is to address people how they want to be addressed.
In business and academic environments in the English-speaking world, it is increasing common to allow people to register "preferred names", which may differ from their legal or given names. For example, many universities have a policy of addressing students by a student-supplied preferred name. Titles such as "Mr.", "Mrs.", "Ms." "Miss", and "Dr.", as well as sometimes "Mx.", "Prof.", "Hon." or "other" are usually available when these names are supplied. There is a long tradition of people choosing to names other than their legal names (there have been historical figures who prefer to be addressed by their middle name instead of their first name). Furthermore, at the present time, transgender and non-binary people are struggling to be addressed as they choose. Given that the situation is evolving and complex, it is best practice to ask what title the person would prefer.
Calling a person by his or her preferred name shows respect.
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In business situations, use formal titles unless the people you meet tell you otherwise.
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In my view, it's not even your responsibility to determine whether this person has the credentials traditionally required for them to use such a title in your culture. They are a respected guest and you should refer to them as they wish, regardless of any traditional rules that you have been taught, which may vary from culture to culture and context to context.
Edit: I'm arguing that a respected guest should be given the benefit of the doubt that the title they've given you is valid in some cultural context. The rules around titles differ vastly between organizations. Doctor is particularly complex since requirements for doctoral degrees differ substantially between disciplines, institutions, and countries. While doctor is equivalent to physician in the common parlance, by US tradition, the title Dr. includes Doctor of Medicine (MD), Doctor of Osteopathic Medicine (DO), Doctor of Veterinary Medicine (DVM), Jurist Doctor (JD), Doctor of Philosophy (PhD), Doctor of Sacred Theology (DTh), etc. It's not your responsibility to obtain their graduate studies transcript and evaluate whether their degree corresponds to your local definition of a doctoral degree or even whether it was valid in the country of origin. If they require you to address them by obviously inflated, pompous titles (although you should be careful about differing cultural contexts), I simply wouldn't invite them.