If 99 out of 100 callers are wrong, are frustrated, and don't know how to clear their cookies, and then you call in, they'll treat you like those 99. Even if you're correct, just cheerfully trying to be helpful, and even if you did clear cookies literally identified the obvious typo in their Javascript that makes it work again or whatever, you're an outlier.
Maybe you can get that person to readjust their expectations for you, maybe you can't, and maybe their management can embark on a massive education and training effort to teach their customer support agents to assume that each new caller is an intelligent expert who's aware of and has already tried the obvious things, but tomorrow they will regress to the mean.
