I'm just wondering if we should even talk to the customer...
There is no problem with telling your customer what the law requires. The difficulty is that you have to limit that conversation and make certain you do not provide enough additional information to be accused of "assisting in structuring." Hence, devsfan's suggestion that you hand out a pamphlet that simply explains the law; the pamphlet is an internal control that makes certain you do not over explain.
FinCEN is working on a pamphlet of its own on CTR filing. (It's finished and going through the final approval process.) I'm curious to see how it might be an improvement over the commercial product.
As an aside, I believe that only a small fraction of the general public knows that large currency transactions are reportable and that an even smaller portion of the total might realize that avoiding the reporting requirement is a crime.
Nevertheless, when the person who gives my daughter riding lessons, trims my trees, or reupholsters my couch asks to be paid in cash I know exactly what is going on and I think everybody else does too. If you refuse to pay people in cash you are innocent. If you do not...