@Nancy1280 While I can understand a guest wanting to check a place out before committing to a long term booking, there is really no advantage to you allowing this, and it's a security risk for you. It's essentially opening your door to a total stranger, who has made no commitment.
The guest might be a thief who is using this strategy to take a look at what might be worth stealing, entry and exit points. Or they will try to get you to rent to them off-platform, so they can avoid the Airbnb fees. I've read posts from hosts who had allowed pre-viewings, but stopped. They wasted hours of time with these lookie-loos, who never went on to book.
Just tell the guest that you don't allow viewings, that they should be able to get a good idea of what is on offer by the photos, listing info and reviews, and that you'll be happy to answer any other questions they might have.
You could also suggest that they just book one night first, in order to determine if they would consider it suitable for themselves for a longer term stay.