I would like to share my experience buying jades from Myanmar, China, Taiwan and Singapore.
Myanmar - home of jadeite - actually did not have the nicest things. The best rough are usually shipped out to Hong Kong for cutting, and then sold to China the biggest jade market of all. I saw mostly spinach green and white stuff at the Mandalay jade markets; the cuts were a bit rough and the polish was basic. My friend however spent a bit more time in Yangon and managed to reward herself with an imperial green pendant. I don't recall how much we paid (their currency was very confusing) but our purchases did not burn any holes in our pocket.
My next purchase, a bangle, was in Yunnan province of China. That's near to the border of Myanmar's jade producing region, so by proximity, Yunnan has A LOT of jadeite. My jade bangle was certified by the Chinese government lab no less, but to this date I'm still unsure if it's an A or B. It was priced as a grade A for sure. I've shown it to dealers in Taiwan and Singapore who say it's a B. In fact they tell me most jades from China are B, so it's buyer beware. Having lived in CHina for many years, I'm fairly used to it when people get suspicious of things from China. That includes the mainland Chinese themselves, that's why many of the rich prefer to fly to Hong Kong or Europe or Singapore to get their LV bags and diamonds and such, they just don't trust their own local sources.
My few trinkets purchased in Taipei were definitely B, B+C and so on. They were just rings and pendants that didn't cost much, and frankly back then I didn't know or care much about acid treatments and colour dyes. Some merchants were upfront about what was A and what was B or C, but there were shady ones who insisted theirs was A and they could issue a cert to prove it. It got a bit hilarious when I did ask for a cert and the seller directed me to the main reception counter. When I got there, the receptionist said she can issue me a cert ONLY IF the seller so says it's A. I went totally like... Huh???
As for Singapore, where I studied and still visit twice a year, the merchants are generally upfront about what is what. Singapore is a place where the trust level is high. However I find the selection of jade to be limited, perhaps because like the earlier posters said, jade is not popular with the younger generation. They think it's old fashioned, or they think it has religious links (you'd hardly see Christians wear jade for example, but the Buddhists and Taoists do). Li Hong and Peach Blossom are the 2 most well-known jade vendors here, but I find their selection to be unexciting and the colours are run of the mill, compared to what you can find on Jojo for example. They stock some modern colours that appeal to younger buyers, but most of their lavender jades are really just the common yam-coloured variety. For that, I think they charge way too much. But Li Hong has nice designs, including square-shaped bangles. If you want a central place to browse and bargain, go to The Bencoolen where most merchants actually hail from China and I do think most sell Grade A, but you need to bargain hard. For me, I'm happy to have narrowed my sources to 3 reliable old-businesses that have been dealing in jade for many years. They've been in the jade business for decades and their wares are of outstanding quality. I won't disclose them here as I don't want their prices to go up astronomically, but if you're visiting Singapore please pm me I'll be glad to share.
My next stop will be Hong Kong. Anyone has recommendations of where we can shop there there? I'm sure Hong Kong is the most sophisticated place to shop for jadeite!