Yes actually. I know a user who only had one post and it was a bangle with a cert saying it was grade A, but turned out to be B+C when sent to GIA for testing. Believe it was Maithong or someone else..
So all in all if you’re really better off going with some sellers listed as reputable, or sellers whom you trust will sell you untreated jade. If you want my personal opinion I’d say Gojade (also their sister shop antijade), chenhantaobao97 (be careful with their images as they make their jades in photos look vibrant than they are in reality), preciousjadeite (she have her own facebook, and wechat account where she broadcasts the jade market she roams around and you can ask her to buy some jades for you and do bespoke options I believe), chineseoldshop (seller has very poor english so miscommunication and reminder to ship your jades is more than likely to happen, they also sell some rather risque products too so proceed with caution maybe

), matsalice (a member here and a jade lover who sells a good variety of jades), Ultimate Jadeite, All About Jade, AAAJadeShop, and Yokdee Jadeite.
The last four sellers always have certificates ready and you can always ask for an additional one if you want to just be sure, and they have some eye-candy pieces with some not so candy-like prices that are for either investment purposes, or to showcase it if you ever do wish to splurge on such luxurious looking jades!