If the only reason people are selling Seau items is to profit, so be it. They are not forcing anyone to buy and they are not stealing from Seau's family. Some sellers might actually feel good about serving Seau's fans with their items - a bonus on top of the profit earned.
So, if you ever find yourself thinking that people are horrible to sell trinkets and other items after death and disasters have taken place, stop and ask yourself who is actually being harmed by any of this. If your only conclusion is that it "feels" wrong then this is a good place to start thinking, rather than feeling so that you avoid inviting government in to help decide when it is moral to buy and sell things.