The phrase 'pig in a poke' is what I had in mind.

I guess 'honest, decent and truthful' is laughably simplistic in todays sales environment. One step ahead of the police is probably closer to it.

I've been buying and using cold-weather sleeping bags since the seventies--before that, too, if you include those gigantic, kapok-filled monstrosities so common before the advent of modern synthetics. That being the case, I can report that you couldn't really trust temperature ratings back then, either. Many companies rated their bags for survival (i.e., you probably won't die during the night at this temperature) but described their ratings as if for comfort.

More reliable ratings could be guessed-at based on measurements of actual loft--same as today, although the manufacturers were apparently very good at fluffing and plumping to achieve maximum measurable loft without much bearing on what happened during actual usage. I note that the link given by the OP doesn't seem to offer loft measurements, and this alone would rule out a sight-unseen purchase in my book. 50 years ago, as today, the buyer had to draw their own conclusions based on whatever scanty data was provided--and tune out the sales staff unless by chance in the presence of one who was both experienced and honest.

I've always discounted temperature ratings by at least 20 degrees F, often more. I've discounted further to allow for damp insulation when appropriate, and further still if not planning to use a tent--a small tent is worth 10 or 15 degrees, a larger tent somewhat less. Then I try to allow for general states of exhaustion or inadequate blood sugar, either of which makes me sleep much colder. My resistance to cold (or ability to generate warmth) has deteriorated as I've gotten older, too. In all respects, YMMV.

Mark