I've had it tried. Corrected it. Since I'm looking for opportunities to promote 2A I usually just declare I'm an average citizen, then start talking 2A.
Don't feel too bad. Maybe next time, if you don't want to reveal you are a private citizen, just thank her and say you know for a fact you are not entitled to a police discount.
My problem is the youngcashiers who want to try to give me a senior citizen's discount! Ahhhhhhhh! I'm not even close to that age bracket. (Not one word, Tomahawk! Not one word! )