Hi @Negar P., congratulations on closing your first deal! That's a huge milestone that will be remembered for the rest of your life! Sorry to hear about the bad neighbor situation, that can always be an irritating inconvenience.
For this situation, I would recommend checking in with the other neighbors and asking how they feel about him and what their suggestions may be. See if your other neighbors are having similar suspicions, it may be something multiple people have to work out.
If you want any luck with getting this neighbor to sign, I would recommend getting to know them and talking it out. Tell them about your new endeavor, and some things about yourself. Be nice, be smart with your conversation. Know what you want to talk about before going in there.
If you think the suspicions start to grow with this neighbor, you can start taking notes and pictures. This way, you will see if this is a real problem or not. Alongside this, if anything comes down to this, you will have a record to show authorities.
Good luck with this!
Leo.