The first and most important teachers in your life are your parents. You don’t only bring their genes, but also a part of their character. This is what i see at least in me, my father, my grandfather. And i have seen that this character is similar to the Croats (at least from what i read from their history).
The language someone speaks and the place someone is born may change from generation to generation, but the genes and the character does not change, at least when not too different between them ethnicities are mixed.
From my experience with people here (and i have seen many, because of my job,coming from almost all ethnic groups you can find here), those of slavic origin are generally more honest than the rest and less cheaters. Some years ago i thought it is a matter of education or something like that, but i have understood it is something deeper.