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Phrase(s): Could I help you? [and] Can I help you?; May I help you?
Could I assist you? (Said by shopkeepers, clerks, food service workers, and people who answer the telephone.) • The clerk came over and said, "Could I help you?" • Clerk: May I help you? Mary: No thanks, I’m just looking.
McGrawhill's American Idioms And Phrasal Verbs