What we should all do is have business cards printed with important chameleon related links that we can hand out to people when we encounter this.
Then in this situation you could simply walk up to the person, hand them a card and say something like, " I keep chameleons. Here are some links to great information about them."
You might also want to tell them to hang onto their receipt in case they need to return or exchange any of the supplies they buy today.
Then walk away.
This is how I am planning to deal with it from now on.
No conflict or confrontation, 20 seconds and you move on.
-Brad