Poloniex is one of the largest crypto exchanges to date, but they take advantage of a legal loophole by not allowing cash on the site, which lets them avoid certain licensing requirements.
Instead of cash they use tether as the primary altcoin to create trading pairs. It's been assumed that tehers have a 1:1 value with the fiat currency they represent. With the recent shady Bitfinex token payoff and the tether prices skewing lower, I'm beginning to wonder if cracks are appearing.
Since Tether is not officially backed by anything and there is no guarantee of trading it 1:1 for fiat, it's possible to over-issue tether and inflate the supply. If that's the case, an abundance of tethers would drive up the price of crypto trading pairs. BTC/USDT for instance, would start to see a price divergence and increase higher than BTC/USD.
That would ultimately make trading prices higher than they should be. On other exchanges, traders would see the prices going up on Poloniex and they would be inclined to match that activity. The only problem is what happens when the markets figure out tether is much less valuable they assumed.