@Craig760
I host long term guests and do occasionally get requests to view the listing first. It's not necessarily something suspicious (unless there are other odd things about the guest's messages) because some people, especially newbies to Airbnb, can be nervous about booking something long term and worried it won't be like the photos/description.
However, I always say no. I just tell them that it won't be possible as it's against Airbnb policy to exchange any contact details prior to a booking being confirmed for security reasons, and that viewings are not allowed, but I'd be happy to answer any questions/concerns they might have. You could also offer to do a video tour, once they have booked.
I would also not want the guest to have my address until the 48 hour grace period to cancel has passed - this is something you can select in your settings).
I did do a viewing with my first long term guest, but only AFTER he booked. This was both to reassure him and me. The second one was supposed to do a viewing too, but couldn't in the end, so we just had a long phone conversation. Now I am more confident and experienced, I don't bother with this anymore, but I do like to have a reasonable amount of information from the guest and correspondence with them before accepting any booking, especially longer ones.
I do ask guests to verify their ID before accepting a booking (I also require them to have uploaded a profile photo, although you can't see this until after the booking is confirmed). It's rarely a problem. If a guest starts to get cagey about doing this, it could be a red flag.