If you sell for more than the device is likely to ever earn, then of course it's better than mining.
The number will be lower than the expected lifetime revenue. You need to account for risk (and at AM level, 0.01% hardware failure or downtime means a lot), opportunity cost (as mentioned, 1 BTC in the blockchain...), and expected ROI for customers (nobody is going to buy ฿100 in profit for ฿100).
In other words, because AM is more efficient at mining than Average Joe, if we are approaching the treshold of sale/mining, I think AM should hold on to units rather than sell.
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What about marginal cost of deploying. Let's say that new datacenter has power capacity for 12TH/s. Is it cheaper to give up part of revenue due to unit selling or give up part of revenue due to new datacenter?