[Gilgamesh]

I think the criteria differs from a person to another...and unlike you said, many people will be hung up on looks,education,wealth,job...or other criteria which hinders the possibility of any affection or love to be born....

But sometimes people are stunned by falling in love with people they might have expected to reject outright from the first moment...

It is a very complicated process that differs from and individual to another....what I can firmly say that it happens at the level of the unconsciousness and we will never figure out what inner cries,insecurities, or flaws a lover answers to qualify him/her to be a lover....