Just because you have an opportunity to do something, and it's not explicitly forbidden by any laws or 'terms of service' or whatever, doesn't make it okay.

Imagine that I went to a store, identified every booster pack with a rare card in it via weight, and then bought all of them. Then let's imagine someone else walks in. This buyer is a reasonable person, but not savvy enough to know that booster packs with rare cards are easily identified. He buys the packs thinking that his chances of getting a rare card are 5% when they are really 0%.

Do you feel that that was wrong of me to do? Or was it the other buyer's fault for not being smart enough to already know that someone like me would have come along and done what I did?