All these 3 articles here under to read, with strong arguments to explain how the BTC value could be manipulated by both bitfinex & Tether:
How would Tether be a ghost coin with no value at all and no guarantee funds:
https://coinreport.net/tethered-to-reality/Story behind Tether;
https://hackernoon.com/the-curious-tale-of-tethers-6b0031eead87Spoofing operation in July on Bitfinex, same author:
https://hackernoon.com/meet-spoofy-how-a-single-entity-dominates-the-price-of-bitcoin-39c711d28eb4All of this seems very serious to me and scaring for the future of crypto currencies trade and market.
Please , do not bash, i'm not a specialist. traders and economist welcomed to comment.