Am I selfish for not wanting hand me downs?

So this is my first baby, and we found its a boy. My SO sister also had a boy who is now 9 months. She wants to give us all this stuff and I am trying not to be mean but I don't want it. I want a NEW car seat, new bassinet, new clothes. I don't want to take the stuff and not use it because that seems ruder. I explained to her that this being my first child I really want to buy new things for him and she should give the stuff to once upon a child, she called me selfish and stuck up, am I really being that way?