The only problem I faced on Poloniex, is the inability to place an order at peak times. In general, I do not have problems.
I have been using poloniex for more than 1 year now, till now I didn't face any problem with this exchange.I have many bitcoins in poloniex exchange where I am trading happily without the problem and when it comes to withdrawal and deposit they will pay on time without any delay, only if they have any issues with their software.
I am also very pleased with this exchange, there are simply situations where you can see that the servers are clearly overloaded.
The real scam is when the exchange crashes, yet there is clearly activity in the background (via cryptowat.ch or other API plugs) Yet you can't trade on their GUI.
This happened with XMR and most recently with STR. I'm done with them. My coins are off their site. They'll Gox soon.
today is 9/5/2017. Poloniex continue scam verision 2. All coin down, XRP 12.300 ---> 7.700, BTS 3.379 ----> 2.200, STR 2.300 ---> 1.600.v.v.and No one can trade. Traders can only look and lose. Reason of Poloniex is DDOS attacked.Again that reason and trader lost money again because Poloniex's fault. We are going bankrupt gradually by Poloniex
They do have a lot of error and trouble these past few days, but in my opinion the rate downtrend of XRP and STR (not sure about BTS, didn't watch them) is because it is their time to go down. The price was pumped several percent for a few days and eventually it will go down sooner or later, although probably they're coincidentally happened alongside with the server's breakdown.
And about the rates, to be fair, actually most alts are going down in reflect to btc price going up