Some form of that statement has to be the most common sentiment on internet forums. I have to plead guilty to having said it many times myself. Why is it so often stated? Most likely, because it seems so obvious. Surely you can’t trust reviewers to know what you like; heck, some of those posters don’t even trust us to be able to hear. The other reason is that it’s true. The problem is how difficult it is and sometimes not even possible.
There are several flaws in that platitude, though. I’ll talk about some of them but without a doubt the biggest one I had no idea about until I became a reviewer. So, I put it as number one on the list.