I am a non-native English speaker. Whenever I travel to the States and I sometimes hear the question, "Can I help you?"
At first, I thought it was a sincere eagerness to help me. However, after a few incidents, such as accidentally entering a wrong meeting room once, I learnt that this question can also mean, "I don't understand who you are or what you are doing here."
So now I am confused if there is also a negative connotation associated with this question and if there is, then how do I understand from the context if this question is asked positively or negatively.
Are there any thumb-rules one can follow to deduce if "Can I help you?" is said in a positive or negative way?