The trick is that they can sell to themselves without cheating themselves. If Cointerra sold a 2TH unit last year for $5000 and it cost them $1500 to develop the unit, then they can buy more units for themselves. They don't need to pay for any additional research, they don't need to pay for shipping, they're not penalized with a 2 week downtime with shipping. So if the miner costs 1/3 of their total end user selling price then they essentially have only 1/3rd the investment cost that an end user would have. Not to mention the benefit of mining earlier.
Now if they continue to sell the units for $5k and it costs them $1.5k, they can buy 3 units for every 1 unit they sell you.
Another trick is to have 2 different companies set up where manufacturer sells the units to the mining company at the same price as they would to any other customer. The mining company can write off the cost of the miners against the returns. A loss will not matter because it is all on paper and the BTC does not change. This is a scam that is legal in the my neck of the woods.