Since it is not an instant Book reservation, you have the opportunity to reach out to the guest prior to approval. I would do so and ask them some questions about themselves and the reason in which they are traveling, who will be with them, etc.
Also, prior to accepting the reservation (should you choose to do so) make sure they have their full name on their profile as well as an ID.As far as a scam, it could be. I've gotten a lot of bogus requests over the years for 30+ day stays, even 6 months sometimes, where they just submit a request then never respond, or try to pay outside the app, etc. However, I have also had legitimate long term stays from first time users who turned out to be great.
The best thing you can do is communicate and get a feel for the guest. If they don't respond, their answers seem odd, o0r they request to do something outside of airbnb policy, decline them. Better safe than sorry.