Honestly I avoid both Bittrex and Poloniex , alot of people had problems with them (long wait time/poor support , force closing coins etc)
I use HitBTC they have monero (never had problems with them , everything smooth

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Yes, please be careful when dealing with Bittrex. They have a ton of problems recently with verifications, support and withdraw. Some are thinking Bittrex did an exit scam or they were hacked and these problems are a cover-up attempt.