> No, there are very few markets in which all of the buyers have perfect information.

This is solved by 5 minute of searches on the web in 99% of cases really. I never in my life bought something because I've seen an ad about it, meanwhile I solved countless of my problems by thinking about the issue and looking for a solution online or talking to people about it

Absolutely! But, you're missing the cognitive part of this. People don't search for things that they don't think exists.