This is probably going to be disagreeable, but I don't think 'putting the shopping cart away' is the best litmus test for whether someone is a good person. Plenty of bad people put the cart away. In a similar vein, I don't think one's degree of politeness tracks whether they are a good person. To be fair, putting the cart away is a norm of courtesy, not a norm of politeness, per se. But anyway, there are plenty of polite, manipulative, bad people, and there are plenty of gruff, to-the-point, border-line rude great people.