it's not so much the case of polite-impolite as a case of personal distance


strangers and people considerably older than yourself you address by Вы and so verbs conguate in plural

a considerably younger person can be addressed by ты

compare to Sie vs du in German

but foreigners are usually absolved from address by ты in the first case

simple people may consider address by ты impolite however courteous you are in actuality