Saying yes or no to a שידוך is a very sensitive topic. Every case is different, and it’s hard to give universal rules. It is imperative to seek the advice of דעת תורה as each case is unique in its nuances and determining factors. Parental advice is also usually very helpful with this, as parents know their son well, have his best interest in mind, and can give insight from an experienced perspective.
A general outlook however is this. The focus during shidduchim is to see if their character traits, goals, and outlooks in life match.
By the גוים, a match is deemed appropriate when the two sides fall in love. This includes attraction of looks, followed by a lust and satisfaction of spending time with the other gender. It’s all superficial. They are blinded by their lust into thinking that they are suitable for each other. Shortly after they get married, the spell wears off. Then they start fighting. He beats her. One of the main contributing factors to this is that they were never suited for each other to begin with. The only thing they had in common was an imagined love.
By yidden, everything is completely different. The focus during shidduchim is to see if their character traits, goals, and outlooks in life match. Another thing to analyze is her ability to run a jewish home, and raise good children. Is she one who loves giving to others? The question you should keep asking yourself is ‘How will such and such affect us if we get married?’
As soon as both sides are sure that they have a clear picture of the strongpoints and weaknesses of the other side, and are confident that they can be happily and productively married, then they are ready to become engaged. The love will come on its own.
Sometimes, boys are concerned that the girl’s appearances don’t attract him. Although this cannot be completely disregarded, keep in mind that as he spends more time with her and comes to appreciate who she is, her appearances will start attracting him more. In fact, this is a relatively common occurrence.
The same is true for personality. If the personalities truly don’t coincide with each other, then the match is unfit. However, this generally cannot be confirmed until he meets her at least twice. Before that, he does not have a clear picture of her true personality. Girls are more nervous on the first date. Many times the color in her personality is hidden and first emerges later on. This is especially true if she wasn’t so talkative. She will usually open up as she becomes more comfortable.
Usually, when unsure to say yes or no, an additional date or two clarifies things one way or the other.