Well do you actually verify the authenticity of your purchases? It depends on the product category somewhat, some categories are absolutely rampant with Amazon knockoffs in a way that you literally cannot avoid by scrutinizing listings or eyeballing it. The first and only PC thermal paste that I bought on Amazon was from an official listing but I was delivered a straight up knockoff. The thermal paste company is a common knockoff target so they provide serial numbers that you can use verify the authenticity of your purchase. The knockoff product had the audacity to include a fake serial number, presumably because they know most people wouldn't bother checking. The knockoff paste is a slightly different shade of gray, but I only know that because I had previously owned a (verified) authentic paste as a point of reference.