How to answer when...?

KDS   Fri Oct 17, 2008 8:16 pm GMT
When somebody says 'anything else I can do for you'? If no, I'd say yeah and that's it. However, would the word yeah actually means there is something I need help on?
wtf   Fri Oct 17, 2008 10:12 pm GMT
Simply: "no thanks."

Why would you answer "yeah" if you know better?