Ofcourse... but that doesnt mean that all foreigners should know exactly how to behave in a foreign country.

If that would be the case - the world wont be fighting. everyone would understand each other.

in general - if The curb-side guys are not working for Delta, then why are they wearing Delta uniform. Just wear something else and not confuse people. Any layman would think that they are Delta employees, similar to check-in agents.