Dunno
Prove it? A boy isn’t supposed to look at girls period unless its on a date or something. Stam looking is assur. Many guys will rationalize that they are looking because they will then find out about the girl and then have it redt. Baloney. By the time this “gazer” gets married he has looked at 1000’s of girls for no reason. A guy who looks will look at the wedding, the bar mitzvah, the sheva brachos, the vort, the lchaim, the bris, the shabbos kiddush and when walking in the street. He just beacomes a big baal tayvah.
Almost all people marry girls they never saw before in their life so there’s no Heter to look. The only Heter would be is if a guy is at a wedding and someone wants to redt a girl to him and she’s there so probably then it would be mutar to look. Otherwise, its assur to stam look at every single girl.
Vlo Sasuru Acharei Lvavchem Vacharei Eineichem is the issur.