Sometime, people help other people because they have good heart but other time they just pure evil. A few years ago is my first time hear "becareful who helped you." I thought that is a rediculus thing since people won't help if they have bad intention. Nowdays, bad intention come in many form not only do bad things but also good deed can masked a bad intention.
If you ever go to hawaii and your car broke down; first, don't believe anyone look although he does look like a mechanic with a big long truck, second, always asked a license card (mechanics, CPR personels, etc), and third, don't easily trust any one who helped you. If you need professional help, call professional you know or your friend but do say thank you and walk away remember mom always said "dont talk to stranger."