What you described isn't even manipulation, it's exactly equivalent to the exchange keeping a big limit buy order on the book at all times. If the exchange deci

What you described isn't even manipulation, it's exactly equivalent to the exchange keeping a big limit buy order on the book at all times. If the exchange decides to take the other side of your trade, and they offer you a better price then you asked for, great! Your costs were reduced. Do they let you withdraw? If yes then they have no more ability to "manipulate" via this mechanism than anyone else. They are paying for it with their finite funds. It's no different than anyone else putting big orders at 1$. The exchange could discount their own fees, but that's just a disadvantage for other traders, not anything guaranteed to keep a price. There's no trust or blind faith here, just knowledge of how order books and exchanges actually work.