in the short term, amazon may be willing to make a loss to acquire customers.

But in the longer term, the rental discount has to at least be balanced by the extra profit from the sales quota. If amazon then turn a dial to increase sales quota (or decrease the discount), they then stand to make significant profit on the captive customer (who may no longer have an option to move away at the same low cost).

I think this type of deal is anti-competitive, and should be prohibited under monopoly laws (i.e., using dominance in one market to leverage another market).