Worst thing you've ever said to a buyer

An expensively dressed woman at a higher end venue comes up to me
and tells me she will give me cash for a substantial piece marked at
$660. if I give her a really good price. I tell her what I tell all
of my clients who try to haggle, if you use cash on a bigger piece I
will pay the sales tax as I figure it saves me on the credit card
fees I would be paying and we should both be happy. She narrows her
eyes and says “No, you don’t understand. I know you all mark up your
prices expecting to bargain and I know you won’t pay taxes on this
piece if I give you cash, so I expect a much better price than that”.
I smile politely and respond that I will be paying sales tax on any
work I sell as it is illegal not to do so. She laughs and says " as
if I would believe that". As I am turning away from scary woman her
husband comes up to drag her away and says “honey, just because
you’re a cheater doesn’t mean everyone is”.

Her husband said it for me.
Karen