I never use known trading site like poliniex i am trading in yobit and i think you can trade and trusted them.. bu honestly they are slow support or delay responce once you sent a ticket it takes 2 to 5 days.. you can also try bitfinex..
Most trader do trade in Poloniex and bittrex both have a lot of altcoin option to trade and they are trusted.
If in yobit you need to wait a reply from support for 2-5 days and then in Poloniex or bittrex it takes 2-5 hours only or even replied immediately, so why you didn't try Poloniex and bittrex? I have good experience there.