Entering the house you should have been in condition YELLOW (you s/b in condition YELLOW all the time). Upon seeing the messes, you should have gone to condition ORANGE (although you didn't see a person, you saw evidence of a person). Upon seeing the person, where he doesn't belong, he is a threat, you go immediately to condition RED (The Fight trigger. This is your mental trigger. "If that person does "x" I will shoot them." Your pistol may, but not necessarily, be in your hand.)*
Like the real estate broker said, when it comes to your safety or offending someone, error on the side of caution. Further, it's your property.
I think that now days, many agencies require first time clients to stop by the office & leave their DL before an agent will show them a property.
*Col. Jeff Cooper's Gunsite Color Codes for situational awareness
Click here to see The Color Code
If your CCW course is good, you will learn this.