This may be more 'personal preference' or 'not used to the climate' than it is an issue of ethnicity.
You may want to install a dehumidifier that guests are not able to turn off, that way you could avoid the mold. Have you considered shutters or blinds instead of curtains, would that help prevent mold? There are some paints that claim to be mold-resistant, that could be another mode of prevention.
You could offer hints in your house manual and/or house rules - for example, "Welcome to River's Edge cottage. Our wonderful climate is quite humid - please, to prevent mildew or mold make sure to [whatever instructions you would like]" Not every guest will read the manual, but some will and at least you will have a defense in the case of complaints.
Also check with local clean freaks, seems like there should be a way to get things clean smelling quickly unless your guests tend to be quite long term, in which case you may wish to build in a few days between bookings?