One of the main focuses people dish out towards how dumb Charming is, is that he falls in love with Cinderella, yet forgets what she looks like. This can be explained by modern science. In the film, the Disney one, not one of the many remakes, Charming acts very bored at the ball. He was just being introduced to countless women who all acted the same. They all wanted to get to know him for his money and power. They would even walk away after introducing themselves.
But then this new girl enters, a girl who is astounded by the castle and the way it looks. She doesn't even have to approach him because he goes to her because she is not only trying to become queen. Cinderella was just trying to find the ballroom, she was not even 'introduced' to the ballroom. After the two spend the night together dancing and talking about everything they want in life, she says she has to leave right at midnight. The two were having such a grand time that they did not need to tell each other their names, names were not important.
Charming might have the brain disorder known as Prosopagnosia. The word means 'Face Not Knowing' in Greek. It affects the area of the brain that allows people to recognize peoples faces. It is also known as 'face blindness'. So he spent the entire night getting to know the true Cinderella, he did not fall in love with her outer appearance. He fell in love with the girl's personality, her inner beauty.
This is where the glass shoe came into play. Only one woman in the entire kingdom would fit it. Glass is not like materials normal shoes are made of. In regular shoes, two people having a size 8 can both wear the same shoe. If you ever looked at the foot people have different shapes and sizes. Peoples feet sit differently. Other women might have been able to put her foot into the shoe, but it would not have been a perfect fit. The shoe was made around a mold of Cinderella's foot. Cinderella's feet would sit different in the shoe making it fit perfectly to her foot.
Even if the shoe did fit another woman, after hearing the girl's voice, Charming would have realized the imposter was not the women he fell in love with. There was only one Cinderella.
If you would like to learn more about Prosopagnosia, you can read about it here.