Dishonest people comes in all forms, they would first gain your trust and loyalty before they strike, but one way i have used to identify them is that they would always be asking for things from you that they are not supposed to, knowing fully well it will be difficult for you to say no to their many requests.
I have accomodated a number of people who i later realised were using kindness against me, I would be responsible for their feeding and they would always say they don't have money, and bring all sort of stories about their work place which made them their bosses to cease their salaries. Before i do realised what they were doing, most of the time, they left without paying back the money they borrowed from me.