The negative trust by these two seems pretty shady to me. I don't think there was any credible evidence of polo scamming in 2017.
Polo was way behind on their support tickets at the time. They also had taken down their trollbox at the same time. I can see where people were getting leery that another exit scam was looming. Polo has since changed ownership, anyway. So the tags should probably be revised. Unfortunately, Zepher can't revise his. 
Read: https://www.reddit.com/r/BitcoinMarkets/comments/8mizvf/dear_poloniex_you_specifically_said_you_wont_hold/
They cant be held to their word and due to that i find them extremely untrustworthy. Imo they deserve to be tagged for this alone.
Also more recently all the people margin trading lost 16% of their margin funds due to sudden liquidations of a single low-cap shitcoin.
Quick maths shows this is nearly impossible and likely some sort of scam
https://www.reddit.com/r/BitcoinMarkets/comments/bxknrf/poloniex_btc_margin_lending_pool_losses/
I can verify both the lies about KYC as well as the margin lending losses. Regarding margin trading, it is a WELL KNOWN tool of market manipulation (read fraud) used to control precious metals prices for example. Also I am very familiar with the Clamcoin market, and it was well known to have a lack of liquidity. This was not an accident it was a setup. This is exactly the type of behavior Cryptsy was exhibiting, in fact point by point. If I remember right Cryptsy didn't have margin trading, but they played similar games with liquidity and other processes. For example they would let people drive up a coin's price then disable the front end so they could scalp the order books via the API which was still active.