Hechsherim are a marketing expense. For example Striets which has the Solovetchick Hecsher had to get a more well known hecsher in order to get it’s product into some kosher stores. People who do not recognize the hechsher will net rely on it and wouldn’t buy it.
Stores try to maximize profit so if they have a choice between two products they will use the more marketable item.
In theory you can rely on any hechsher because a Jew is believed as to what is kosher. But this person is being paid to do it so it is quiet possible that for money he might lie. That is why you should always rely on a reliable hechsher.