You know what? Honesty's the best policy, right? So let's be honest:
>"Actually, I took that first one because, well, everyone's been calling the beads and gems and such rocks, so, hey, innocent misunderstanding. That's why I was more specific when you walked up."
>"But, well, I guess I can understand where you're coming from. As soon as I have a moment, I'm going to make a sign saying what precicely I'll be accepting."
>Hand her a bottle of something in the 10-20☼ range.
>"In fact, how about doing me a little favor? I'll get the sign done, but while I'm doing that, could I get you to just tell people I'll be ready in a minute?"