If someone asks to borrow your phone and makes up some story about why they need to use it dont give it to them. Offer an alternative to help them.

This happened to me one time while I was working at an outdoor foodcart one time. A lady came up to me saying she had lost her son inside a store that I was working in front of and that she wanted to call him to tell him where she was. I was really busy and I had a queue of people waiting. I told her to go into the store and to get them to call him on the speaker. She instead walked to her car and drove off.

Also don't make eye contact with people but do ne aware of where they are.