Agency relies on the owner?! Thank you very much, I can rely on the owner myself, why do I need an agency for that?! The agency, I think, is supposed to provide independent assessment.
Interesting question about geneiva. Yes, such a person can testify about kashrus – but would this only apply to someone else? If it is his own business, then he has monetary interest and that is why we have an agency to begin with. So, not sure this would work.
In general, our generation is more careful about kashrus than geneiva, so we need to be more careful and check our biases. I already recounted here a story about a visiting speaker who went thru lots of business halochos: very machmir on kashrus and yichud, and very meikel on very basic geneiva where there is no need to be meikel (can you double bill your clients for a trip? not really, but sometimes …). I was embarrassed to ask about this difference publicly given enthusiasm of all listeners and was relived when Rosh Kollel picked up on this and started shouting – geneiva! geneiva! I asked the speaker later in private and he explained that he is strict on problems that sometimes lead to family breakups, but wants to let yidden have it easier when things are not that serious …
so, ironically, I presume if you find pork in the store somewhere in the corner, it will lose certification because of a hashash; but if you find wrong weights – isur in the Torah – he may not!?