How do you spot a woman who is an opportunist?

Some women especially those who do not have a good job or who has a really bad family problem like a lousy husband or boyfriend who is not taking care of their kids or is being abused, would push themselves on a man who has a good paying job. They don’t necessarily love the man but would more often try to fool him or trap him in some way. I have seen this and actually I have been told this by a lot of older people and have been cautioned to be put on my guard. What I want to know is how can a man tell? Is there signs that he should look out for?