There are gold shops selling necklaces and rings on the streets of every town and city in Thailand. The gold on sale is 99.99% pure, which is of a much higher quality than you will find in western countries. Gold is sold by weight and the unit is the Baht, the same name as the currency. One Baht is 15.2 grams. The buying and selling price of gold is quoted in the newspapers such as Bangkok Post on a daily basis and the price in the shops will be very close to this. In addition there will be a small charge for the workmanship, generally only a few hundred Baht, depending on the size and weight of the item.
These shops will quote the buy/sell price, which is often on display, and offer a genuine market as a necklace can be sold for cash, or traded in for an upgrade to a heavier weight at a later date.
Gold shops will often accept credit cards though they may ask for a surcharge of 2-3% as they are generally a cash business.
Thailand does, in theory, offer bargains on gems and jewelry, it's just that buying them is such a risky proposition that it is not recommended unless you really know what you are doing. If you are planning to purchase, the comments below should help to ensure you are not ripped off when buying:
When reading about the gem scam, it's easy to assume only gullible people get taken in by it. However it is done in such a sophisticated way, with so many seeming coincidences, that a lot of people fall for it even after reading all the warnings. Be aware that the con men are not above dressing in official-looking uniform to try and get your money. Every citizen in Thailand has an ID card, with the details written in Thai. If someone recommending you buy gems from a particular shop tries to show proof that they are from the Tourism Authority of Thailand or some government department, the ID is probably meaningless.
It is not really in the Thai culture for a lone person to approach a stranger or strangers and start a conversation. If 'normal' Thais do just want to talk to tourists, it is almost always done in a group. Therefore if you are approached by a lone individual, particularly one who speaks English well, be very wary. It's also worthwhile looking at what the person talking to you was doing beforehand, as very few people without ulterior motives linger alone outside tourist attractions just hoping for a friendly chat.
This is basically common sense as few people would talk to strangers on street corners in their home country, but they let their guard down with the relaxed atmosphere in Thailand.
The Thai government and/or the Tourism Authority of Thailand (TAT) does not own, sponsor, promote, endorse or authorize any gems stores in particular, and anyone who tries to tell you otherwise is lying.
It is impossible, even for a qualified gemologist, to tell the difference between genuine gems and a clever cut-glass fake without the proper equipment. If you buy without getting the gems tested independently, you are buying solely on the word of the shop. The National Gem Institute is planning to open booths at shopping malls where the authenticity of gems and jewelry can be verified.
Real gem shops very rarely offer 'sales', and 'one day only' or 'export special' deals are definitely a scam. Never agree to mail gems out of the country, however much the shop may try and persuade you. There is no export duty on gems or jewelry so there is no reason not to take the items with you.
If you are buying gems, you're well advised to simply buy for personal use the ones you like the look of. Buying with the intention of reselling for a profit back home is a recipe for disaster.
If you have been scammed we recommend that you contact the Tourist Police. You may be able to return the gems and get some of your money back. If they have already left the country however, you have little chance.
It's worth buying only from members of the Thai Jewel Fest Club, which is a non-profit organization set up by the TAT, the Thai Gem and Jewelry Traders Association, the police and the government. Members have to abide by a code of practice, which includes the provision of at least 80% refunds up to 45 days after purchase. The members are all reputable vendors and though it is impossible to guarantee there won't be any problems, it is much, much less likely than at a random shop a stranger takes you to.
The Tourism Authority of Thailand has more information and a list of members of the Jewel Fest club.