Hello @Anonymous,
You can message him and ask him to go through the ID verification process.
You can also ask general questions like what brings him to the area, why the repeated stays etc.
You can then get a better feeling about him from if he responds, the tone of his responses etc.
As you have instant book turned on for your listing you can also set the requirement for guests to be ID verified and have recommendations from other hosts. If you set the ID requirement you'll have to be ID verified yourself.
If you have these requirements then only people with those can instant book. Otherwise they have to send a reservation request which you can accept or delcine after messaging them for more information.
Steve.