^I'm sorry but that doesn't make any sense to me.
If you saying that sales of a book is the only way to determine if a book sold well, then yes I can understand and agree with that statement.
If however you are saying that sales is the only way to judge "the majority view", first of all I don't know what you meant when you said this.
I'm going to guess that you meant how a book is received by the readership at large.
Sales does not mean people liked your book, approved of your book, enjoyed your book, or even READ your book. Sales of a book just means that someone bought your book. Now, in terms of financial success, sales are a positive indicator.
But in terms of worth, value, quality, craftsmanship, etc., "Sales" (a quantitative measure) is not a good indicator as these are all qualitative measures.
I'm not opposed to looking at sales data, but I know for a fact that sales have in no way any bearing on how a story should be judged.
For example, from what I've heard, AotF didn't sell well, however, from what I've read, it happens to be regarded as a fantastic book and I'd have to agree with that.
Harry Potter & The Deathly Hallows, sold a jillion copies, and one of those happens to be on my shelf in the corner right now. I bought the book, I read the book, but I didn't think the book was that good in the middle and if not for the ending, would've been a waste of a good series.
Honestly we're not getting the sales data regardless so the whole thing is mute anyway. I mean, sure... I'd like to see what trends there are right now in buying patterns and track the rise of certain series over the years coupled with the introduction of certain authors, but even if we had it and it told me that "Before Dishonor" sold a million copies, I still wouldn't like that book. Opinions matter, especially in the world of literary fiction.