Close second to my previous:
"I'm sorry...I can't sell those parts at that price. They aren't the same."
Said (approximately that way) several years later at another job. The manager I liked had just left and a new one came in. Part of his sweeping business changes was to get rid of our reliable vendors and reliable parts and expected us to sell cheap crap parts at the same price as the old. Two of us were let go for having ethics.
Then sued for using proprietary information, misleading clients, theft, contract violation, anti-competitive practices, etc.
Last seen the new boss had sold his house, closed all his businesses in the area, his lawyer (who was his BB in high school) wouldn't take his calls because he refused to pay and the company I had worked for was given to one of the vendors for failure to pay over $30,000 in invoices...I won't get into what happened to the company the other tech, myself and a mutual friend started.