Yes, expectation bias is real, but not for significant changes. And when ever I buy a new piece of gear, I have no expectations because I have been disappointed with audio gear, more than I have been pleased. So I try and go in with an open mind and a clean slate. When I was at that dealership house and he pulled out this $800 power cord, I was expecting to hear an improvement and we heard nothing. You can't blame everything on expectation bias or psychoacoustics as the deniers would like you to believe.
I got into a discussion on the Steve Hoffman forum about hearing differences in dacs. And this condescending ahole who tried to belittle me and was totally disrespectful said it was all in my head. Yeah, it's in my head that my Luxman has a warm, lush sounding compared to all the other dacs that I have had in my system. Or that the Exogal Comet that I reviewed for the company had this expansive 3d and holographic sound stage, same for the new Van Alstine dac. Same for the highly touted topping E50 dac that the ASR guys touted which I use for TV but it sounds bright, veiled and thin in my reference system. I guess that was all in my head.