Psoodonym I see where you're coming from but the fact is that a lot of people get consistently different effects from different batches of MXE that has been tested to be analytically pure. As in, I CANNOT get the same experience no matter how high I dose. So it is not simply a matter of purity (for example, if a batch was simply 20% less pure by weight).
I don't think expectations come into play too much here because I always have high hopes for a new batch of MXE. In fact it took me many uses to realize that it was simply not giving me the same experience I was used to. So perhaps it is true that at first, the placebo of thinking it was a high quality batch made it seem better than it was. However I eventually noticed a stark difference when one day I tried a bag that I thought was just as good from a month ago. As someone said, it's like the difference between grape juice and wine. The effects were so different that I still wonder if I have different drugs, I just don't have the money to get multiple samples tested right now. Maybe in a few months, but that's hundreds of dollars for something that may just say they are all just MXE..
It's not like it's keeping me up at night worrying about it, the point is that it makes purchasing MXE very difficult. I'm buying it because I want the magic feeling. When I pay a big chunk of money for a bag of magic and the magic isn't there, we have a problem. The problem is exacerbated when the MXE is actually analytically pure. Because then the source isn't actually selling 'bunk product', so even an honest vendor has to get rid of the stock.
I talk with my vendor about each batch and when there have been problems with 'no magic' in the past, he always reported having other people message him about the problem as well. Do you really think we are all having paranoid delusions at the same time about the same exact batches, or is it perhaps more likely that there really IS a reason for variance in analytically pure batches?