Fascinating article in Lapham's Quarterly by philosophy professor Clancy Martin, who worked as a swindler in a crooked Houston coin shop in the 1980s.

I took the ring in back and showed it to our diamond man. "Hmm," he said. "Go put this one in the ultrasound and then give it a good steam. Bring it right back." After I'd steamed it, it was blazing. It must have been a family diamond.

"This is a diamond. This is a seven-thousand-dollar stone, our cost," the diamond man said. "Offer her two thousand. Buy it, Clancy. Don't let her walk. I can dump it today for five grand, or we can put it in the case for ten."

….

No, no, no," my brother said. "Have you seen the girl?" He pointed through our one-way glass mirrors onto the showroom floor. "She's desperate." He took the ring from me, rubbed it thoroughly in an ashtray, looked at it, rubbed it again, blew on it, and gave it back to me. Just like the old cigar-smoke trick with the counterfeit coins. "Five hundred," he said. "Not a dollar more."