It was the end of his holiday and he was looking for a gift for his fiancée back in Ireland. Six hundred euros ($820) seemed a bit steep, but he was assured that the gem was worth four times that in Europe.
Only after he left the store did he have the sinking feeling that he had been scammed, something that was confirmed when he visited an appraiser in Dublin.
For most of the 20 million people who pass through Thailand annually, scams are not part of the experience. But for the few who do get tricked, it can be a painful reminder of the need to tread more carefully.
Thai authorities have set up fast-track courts to address tourist issues, including scams. Since its formation in September 2013, the court has handled 245 cases.
"We are working to reduce scams in the area by informing locals and tourists about the crimes and what legal action they can take," said Nattanan Jaisue, a legal officer at the tourist court.
Yet despite campaigns to increase awareness, scammers continue to find ways to profit from unwitting tourists. Here are five of the most common ways they do it:The Grand Palace is closed
The Grand Palace scam is one of the oldest in Thailand, so popular that it has come to symbolise naive tourists.
The scam begins with a tuk-tuk driver telling unwary tourists that the Grand Palace is closed for the day, followed by an offer of a free ride to see the sights. The scam ends with a visit to a gem or jewellery store where products are sold for vastly inflated prices.
Scams involving worthless gems have become so problematic that the Ministry of Tourism and Sports has even set up a special kiosk at Suvarnabhumi airport to help tourists who have bought fraudulent gems.
"Tourists usually file a complaint at the airport about the jewellery they bought in the city before leaving the country. They are usually unsatisfied with the quality of the gem. We help them by contacting the shop to get a full refund for the tourists," said Pol Capt Kamol Chanpetch of the tourist police division.You damaged my jet ski
A common scam at the beach involves jet ski renters who claim that tourists have damaged their watercraft. The jet ski lenders demand compensation and threaten to call the police.
Unbeknown to the visitor, the jet ski was often damaged before the rental.
Despite the scam being relatively widely reported, it still happens frequently in places like Pattaya and Phuket, with tourists often desperate to recover a passport or other document left as deposit.Trains are full
One of the lesser-known scams occurs at Bangkok's main train station, Hua Lamphong. Phony agents in the area outside the station offer to help tourists book their train tickets, only to claim that the trains are full and that the tourists will need to travel by tour bus instead. In fact, the fake agents just want to sell bus tickets.My sister is going to New York too!
This scam begins with an innocent question: "Where are you from?"
It is followed by exclamations that a relative will soon be travelling there. The scammer asks the tourist to answer some questions for his relative, and once the tourist is comfortable, the scammer tells a sad story and asks for help paying a medical bill.Free ping-pong shows
Thailand's red-light districts often feature touts advertising free ping-pong shows. Once inside a bar, the tourist is shown a menu with one set of prices. When the bill comes, showing massively inflated drink costs, the bar staff returns with a different menu.
"[My boyfriend] went to pay the tab, which was 200 baht for two drinks, when the bar lady gave us a bill for 2,000 baht," said Dannie Higginbothom, a tourist from Minnesota in the US. "The lady said it was for the show but that's not what was advertised. I'd say we were only there for about 20 minutes or so."