The problems with ignoring every signal but price should be obvious.

How many people understand whats important in a roof joist when they are having their new home built?

I think a more subtle, and perhaps salient, question is how many people not trying to sell something understand what's important? It's very easy to mistrust the motives of someone trying to do customer education.

You're right. It's obvious that price isn't the only signal. But perhaps it's more readily comprehensible in many cases, especially when other signals are potentially less trustworthy.