How can i tell the person if he is bad or good by talking?

It is actually very easy.If he is bad,this is the reason. The first thing is to see if he talks sweetly to you and the second is to ask him/her about himself/herself but if he/her gets suspicious then ????? oh well maybe just don't try to get him/her suspicious about you or maybe just maybe if he/her ask you just gave an excuse about something.If he is good, then i don't no the reason.Well maybe i know the reason but i forget about it. Nowwwwwwwww.