If the person that switched his lot to the seal had the item he originally was letting on drop, then he would not have gotten to roll for that item, right? You agreed that he could roll for the seal, right? You understand that your chances of getting the seal were exactly the same and aren't any less just because another player's chances are higher.

I honestly can not understand the difference between joining a group with four people that need seal for themselves and joining a group where three people have agreed to roll for one person and another person is rolling for themselves. That person would have the exact same chance at winning the seal regardless of what the other players decided to do with it.

The only thing they did that was "wrong", was trying to hide the exchange. Even then they are not required to get your permission or inform you of their intentions.

I'm sorry you feel like you were wronged, but nothing unethical happened.