[anstosa]

Ansel from PSL here.

That's not quite right. Ad pricing is a marketplace like any other. The "demand" in the marketplace is demand by advertisers to get in front of any particular set of eyeballs. The price will be high if many advertisers are interested in the same group of people (and low if not). Price is an important metric for determining customer acquisition cost but you can't use it to infer customer demand. You instead use impressions, click through rates, and conversions rates to do that.

[lxchase]

Generally correct, but do watch out for some recent changes by Google, where you pay what you bid instead of being charged the lowest next bid even if you set your bid higher.