It is true that between 70% to 80% of the world's rubies come from Thailand, but don't purchase any there. In Bangkok, this scam is extremely famous, complex, and effective. Not only are tourist police, tuk tuk and cab drivers involved, but often fake English speaking Western tourists. These people all earn a commission for getting you to one of these shady gem shops.

One common experience is based on a bundle of lies told and verified by numerous people at multiple locations. These thieves will tell you that the museum is closed for National Buddha day or some other made up holiday. Then, they will redirect you to other tourist spots all over town where you will meet many other actors posing as gem shop customers.

These tourist impostors will show you fake receipts, claim the gems are easily liquid, and worth twice as much wholesale. And they will tell you that they have been buying and reselling the gems for years. And they even might add, that they pay for their whole vacation with the profits.

Once at the stores, a sales clerk might issue you a certificate of guarantee, but make sure you check their refund policy. And even if they guarantee a full refund, don't buy anything. If you pay by credit card, Visa and MasterCard will offer little protection.

• Golden Argosy Export Center, Look-Luang Road, Mananak, Dutsit, Bangkok 10300
• Sapphire & Diamond Centre, 28/10 Worajak Road, Pombrab District, Bangkok
• SNP Jewelry, 386 Visutthikasat Rd, Pranakorn, Bangkok 10200