We are supposed to know them by their fruits...unfortunately actors are good at faking these. So no, noone can 100% say that someone else is saved. It's usually obvious when someone is not saved, but judging the righteous is difficult at best...I cant see when someone is saved, unless I get to know a person and witness the Holy Spirit in them...I believe we are supposed to give those who claim Christ the benefit of the doubt unless we are shown something else? I know that some of the most ungodly people, I have known, called themselves "minister" pastor..etc... and most all of them could put on a pretty good religious show before others...but in heart they hated the authority of Christ, over His people.