They do not have much liquidity at all on BTC/USDT markets. USDT/USD is listed at bitfinex and has a solid peg at $1 there, to be completely fair. Coinmarketcap displays data that appears biased, though, if you look into the quoted exchange prices from Poloniex on BTC/USDT. CMC would lead you to believe they are actually trading for $1 exactly while the numbers do not add up.
I think some of the players from Tether are just able to pull a few strings to help their image. Our product is speaking for itself like these prices on Shapeshift.io show.
