Sure, but this applies to any sufficiently advanced conspiracy theory and wouldn't be limited to markets. Secondly you the individual can just not buy the shares if you think they are overvalued. You're confusing your own interpretation of the valuation of some company with "the right valuation". Maybe you're just wrong and they're not over valued? Maybe you're right? It doesn't matter much, except you can buy shares in companies that your investment thesis and modeling suggests you might buy.