I've had a couple of runs that made me uncomfortable, one time I was sure I was going to be robbed, two guys came over and one moved to block the front door when we moved in so I immediately looked to the back door and shouted "what the f$%&"? I exited through the back door before they could figure out, I told them something was stolen from my back porch and I started to dial 911. I told them they can hang around, but they left immediately and never heard from them again.
There was another instance when I tried to evict someone and the boyfriend of the couple went berserk, acted in a threatening manner but I kept my cool (and distance). I told him to cool it right now because "I won't tolerate it" and eventually he calmed down, sometimes you worry if someone is on drugs or something and snap, it's a chance you take being in this business (or almost any other business).
few tricks I learned over the years and these could apply to many situations:
1. Always tell someone that you'll be at a property, ask them to call you every 10 minutes, and then say out loud..."OK, I'm here, come on over..."
2. Let the prospective tenant know that the neighbor/realtor/friend may be dropping by "some papers" or something and you may have to excuse yourself for few minutes.
3. Keep back and front doors unlocked, don't let your car be blocked, if it's evening or later, turn a bunch of lights on and make it look like something is going on. Arrive early and see if you can spot a neighbor to chit chat with, etc.
4. Trust your instincts, if it doesn't sound or look safe, just make an excuse and walk away. Phone are great for this, act you received an emergency "text" and just leave.
5. Numbers matter! Ask a partner, a friend, or a relative to accompany you. You can also announce that you have another tenant is coming to a showing.
Most importantly, you shouldn't be showing a place until you have received and verified some basic information from them. Ask them to drive by the property and if they're still interested, to give you a call, you can obtain some information then and verify it's accurate. I've had little chit-chats with people just to get a sense of what type of person I'm dealing with. When I ask where they're coming from or why they're moving, I use their answer to start a completely new line of conversation just to get them talking about themselves.