This is... an understatement. I would agree advertising is a useful signal, but I would say that not only can you not trust advertising, you should put negative weight on advertising - i.e. whenever you see an ad, that means the company is putting some amount of money into trying to convince you by means other than an honest comparison/spec table, and therefore is likely to have an inferior product. So personally, I generally avoid any companies/people whose presentations contains no information about the objective characteristics of their work.