Either it was a glitch (error) or it wasn't. You just said it wasn't a glitch. If it wasn't a glitch, that means that it was listed as free on purpose. If that was the case, then it is extreme for them to blame people for buying content at the price which Microsoft itself set (free).
No people here, not even you, are denying that Microsoft has the ultimate power in this situation. They set marketplace prices, they set marketplace access, they programmed the market place, they selected how people can or cannot access the market place, you connect to their market place through their systems. Using no outside tools, only those provided directly from microsoft, people found a way that when they reached the checkout page, microsoft listed the cost for the items in question as free. Microsoft programmed the system, and using only the system at hand (no outside code or tools) people found a way to get to the checkout page, where price is 100% controlled by microsoft, and end up with a free product.
Now, you are not comfortable with doing that. That is fine, you have the priviledge to choose your actions and what you are comfortable with. However, you choose to attack, belittle, and harrass those who have. You look down on those who have done wrong, yet you take pleasure in making other feel bad and harrassing them. What sort of commentary is this on you as a person?