If I'm asking you questions it's obviously because I need information and if you're representing this company, it's your job to have some knowledge so that when people like me come in asking questions, you then can provide me with answers.
There is nothing more annoying then when this happens and the employee gives you attitude, looks at you like "why are you asking me?" I give that person some time to snap out of asshole mode (I try to remember that at some point this person most likely wasn't an asshole but that being a product of his environment *9-5 probably has something to do with it, seeing how 61% of Americans are unsatisfied with their jobs, isn't that sad?) and if it still continues? I like to calmly lean into them with a smile and say "are you in a bad mood today?" As I pout my bottom lip, Watch how quickly their tone changes.
Keep your cool, wish them a grrrrrreat day and give them a wink on your way out.
Back to you Bob.