Who to Trust?

I find that I really struggle to trust people that I don't know very well.  I'm not sure if this is just me and I have serious problems, or if it has to do with the world be live in?  Maybe it's a little of both.  Let me give you a couple examples.

Yesterday I took my kids to the library.  As I'm loading them into the car a gentleman in his late 50s, starts asking me questions about my car and tells me how nice it is.  He seemed very chatty, I didn't mind talking, I like to talk.  But as he continued to talk, this is what went through my mind:  Why would someone be telling my how nice my mini-van was, this is not a typical car that people admire.  There seems to be no one else in this parking lot.  Why does he keep staring at my children?  Maybe he's the missing murderer who kidnapped and murdered that young girl over a year ago (whom they're still looking for).  Panic obviously set in, so when he took a break from talking I very casually buckled my children and drove off.  He did smile and wave as I drove off, so I did the same back.  Pretty sure he was just a nice man who needed someone to talk to, but I wasn't going to risk it.

Here's another example, about a month ago I was getting groceries by myself.  When I was loading my bags into the car, one of the guys who works at the grocery store (I'm assuming he was out there getting ready to put some carts back inside), goes to my driver's side door and begins to open it.  Well I totally panicked and was completely speechless, because all I did was stare at him.  I thought he was going to try to steal my car until I realized I still had the keys in my hand.  So, he stands there holding the door open and smiling at me, at this point I'm pretty sure he noticed my eyes popping out of my head in complete shock.  Because then he says something about how there aren't very many polite people left in this world.  Then I breathed a sigh of relief, sat in my driver's seat, he gently shut the door and said "have a nice day."  After getting over the complete shock, I was moved by his gesture of kindness, and AMAZING customer service.