Some big box stores have very strict ethics rules fo their buyers and managers that state they can  not accept anything from suppliers including samples or meals. They require suppliers and people they do business with to post those rules in their factories or offices so there is no excuse. Any violation results in firing or suspending business. Very simple. If they do go to lunch, it must be Dutch.   This is what our politicians need to do. We may need to explain it to them several times though.