Hi Wendy, It would be good for you to find some silver findings there - I think that would be better value than looking for pearls in Thailand. I have been there half a dozen times, always for holidays, and it is a great place. Gemstone/jewellery scams are absolutely rife, and upmost care should be taken of anyone offering to take you anywhere. Oh, and the taxi drivers are allowed to kick you out of their vehicle if you don't want to go where they want to take you - sounds like the reverse of what should happen, I know -... which usually means to their tailors/jewellery stores etc... often telling you that the attraction you wanted to see is closed for 'nationals only' or 'national holiday'!!
That said, some of the world's biggest jewellery houses buy their silver in Thailand. A bit of research would be in order!
Gold in Thailand is usually 22 ct.
I wouldn't be buying anything like jewellery at the Bangkok weekend market (Chatjujak) - it is a fun market to visit, and absolutely huge - a must to go and see monkeys and snakes being sold in the marketplace! Great for knicknacks though.
Have fun, Thailand is an amazing place!!