Example: They buy 1GH of mining power for 1BTC.
Instead of waiting for the 1GH to generate 1BTC they sell it for 1.2BTC.
Then they use that 1.2BTC to buy another 1.2GH of mining power.
They sell that 1.2GH for 1.5BTC.
That 1.5BTC they buy another 1.5GH.
Now they got 0.5BTC and 1.5GH of mining power. They sell that 1.5GH, buy more GH and it goes on. Hope you understand me.
I understand you, but you are ignoring the people they sell the GH/s to. Show me how the customers make money in your scenario and I'll show you why cex.io is losing money.
Say they buy it for 1GH/1BTC and sell it for 1.2BTC/1GH. It's simple
Well, they can't buy it for 1 BTC if cex.io is selling it for 1.2 BTC in your example.
Anyway, I don't know how to make the point any clearer: If 1 GH/s can mine X BTC, then it doesn't make sense for cex.io to sell it for less than X, and it doesn't make sense for a customer to buy it for more than X.