Should and does are two different thing. There are ways to get certified/reviewed well yet sell crap. The practise is common enough to have its own name: http://en.wikipedia.org/wiki/Golden_sample

That is why 80Plus has a procedure where a member can challenge that another manufacturer isn't adhering to the tested standards. But it costs quite a bit of money and nobody wants to rock the boat because everybody knows almost everybody has a model or two which are targeted at low price market segments and marketed above factual ratings.