I don't believe that this is in any way formalized. But as far as the last part of the question, it should be possible to rely on it if the company is known to be reputable and follow religious norms. In general we say 'Eid Ehad NeEman BeIsurin ("one witness is believed in (matters of) prohibitions"). Thus, technically, if the producer of the food is an upstanding, religious person, he can be relied upon to state that his food is Kosher. The only reason we have come to rely on outside agencies is that there have been cases in which one's interest in his own product has compromised his believability with regard to the Kashruth of the product. Since the Berachah is not part of what helps the company sell the product (as opposed to its being Kosher), I would trust the label unless I either know otherwise or suspect that they are not reliably educated enough to make such a claim (not that I would suspect them of deliberately misleading me, as I might if it were a Kashruth claim designed to help sell the prodcut).