@Alexander993 It really isn't advisable to let guests "preview" the property. Many guests ask to do this because they want to try to make a private deal outside of Airbnb, bypassing the service fees. They can also be people who are criminal types who want to scope out the property so they can come back and rob you.
Guests should be able to ascertain whether the place is suitable for them by looking at the photo gallery, reading through your listing description, and asking any questions they might have before booking. If they are looking for a place long-term, it's more understandable that they might want to have a look first, but in that case, you could suggest that they just book one night before deciding to book long-term to make sure they like it.