Yet, sometimes the house does not show well when it is foggy or dark/rainy. If you can politely reschedule and not to loose that appointment entirely, it is better reschedule:)
The first impression is very important when meeting people or checking the house.
When a buyer would still wants to come through in bad weather, I would look at that as a sign they are committed to finding a home. It's completely understandable when weather hits to change plans, but I would look at it positively.
As listing agent...still let them come unless the house is occupied and the seller is having a medical emergency or death in the family.
KK German, Wainwright Real Estate