It's difficult to assess really. The website Link hidden: Login to view doesn't have any contact number, but it seems to be very well established in Thailand, and has been online since 2002. Link hidden: Login to view
However I haven't seen any review about them online. And they claim to be an eBay Powerseller but I wasn't able to trace any eBay account under them. I tried calling on the numbers I got online, but they are invalid. If you have any way to reach them to confirm their eBay account, then we can somehow see how they deliver.
Sorry I wasn't able to provide much help.
There are several silver jewelry suppliers in the SaleHoo directory. Let me know if I need to gather a list. :)