What are the most clever scams you have come across?

Mine was in Thailand. I've been in sales for 10 years, and nearly fell for this one. It was that impressive. It's also known as the "gem" scam.

My buddy and I were going around with a Tuk Tuk driver, and went to a smaller temple in the city. We walked around while the Tuk Tuk driver went to the bathroom, and upon waiting for the Tuk Tuk, a person standing at the exit with a camera dressed like a tourist said "Hi" to us. He said he was also waiting for his Tuk Tuk driver.

The tourist: "Where are you guys from?"
Us: "San Francisco."
Him: "I used to work at HP. San Jose. I loved the Bay Area" (in perfect English)
Us: "That's awesome. Loving Thailand?"
Him: "Absolutely. Today is pretty sweet too. Going back to Singapore soon, so I picked up a gem to resell."
Us: "Why would you trust gems here?"
Him: "Oh. Once a year, we come to Bangkok to buy a gem or two. They allow up to only 2 gems tax-free per year, so we buy it at a low cost and resell for about 2X. Pretty sweet deal. You might as well check it out."
Us: "Oh... Ok." (We were doubtful)
Him: "Well, enjoy the trip guys. Bangkok is fun. Make sure to explore X, Y, Z, etc."

The Tuk Tuk driver came back and asked us where we wanted to go next. We then asked about the gem sale. He said "Yes! Today is actually the tax free day for exports. You can only pick up 2 gems though. That's why you see so many tourists from Asia here buying gems to resell."

We were like hmm... seems fishy. However, let's check it out. The Tuk Tuk took us to a diamond jeweler in the jewelry district. We went into the store and saw other tourists coming in also. I think a few of them weren't really tourists, but were actually part of their plan.

Inside the jeweler, they memorized a lot of things about San Francisco. They were able to spit out random companies, locations, popular spots, etc. to build reputation. They didn't even talk about the "tax free day." We then asked about it.

"Why yes. Today is a special day which is why everybody is buying."

Because they did not hard sell us, I started thinking... "Hrm.. maybe it really is true and they don't want people exploiting it."

Nonetheless, we did not buy anything because the gems were ugly. I then googled the scam, and can't believe I fell for it. They have everything perfectly scripted, timed, and tested/mastered. I was impressed.