i think they watch and learn from each other. so if one raven likes you, chances are others in the area will like you, too.
i don’t think birds get discouraged that easily. if it was really trying to give you a gift, maybe next time it’ll bring something different.
here’s a nice story about a girl who collects the things that her crow friends bring her: https://www.bbc.com/news/magazine-31604026.