You're voluntarily talking past their point to lick boots and win an argument around a domain of knowledge that im sure you feel very confident in. The $31 'buy now' issue is a secondary point to the story that demonstrates some of namecheaps incompetence and sets up the situation for the main issue. I dont know why you're reading the rest of their story this way, but it reads that they were more than happy to continue the sale at the original price and didn't expect a finalized transaction at $31.

The main issue is misrepresenting errors on their side as legitimate transactions to communicate to the seller, which works exclusively to their advantage instead of acting as a neutral broker.

There should have never been any financial insight on the sellers side that they were willing to make a 125x markup because that misrepresents the reality of the situation: they were always willing to pay around the original listed price and saw the discounted moment as a suitable moment to act. In spite of this discount being their mistake, the poster still wanted to purchase at the original price. This then allowed them to misjudge the motivation of the customer and poison the sale by renegotiating to a higher price because of this perception, which they were never interested in doing. This also puts them in a strategically worse spot since some of their cards are now on the table.