When pulling off interstate into an unfamilar urban area for gas or supplies whatever if you start seeing vacant or run-down buildings, that is a clue. Graffiti and stores and private residence with bars on their windows and doors is an even bigger clue that you don't want to be there. I also don't let my gas tank get too low where I have to get gas NOW. while you are looking for easy access and departure from the pumps look for people loitering around station. I pass on these also because I have gas to go a bit furthur down the road.
