The word “rabbi” alone is not sufficient, for not everyone presenting
himself as a rabbi really is, not all rabbonim are kashrut experts,
and not all those who possess the knowledge are out there in the
kitchen getting the job done. The legitimate rabbanim doing the job
are the first who will verify this.
The title alone is no more a guarantee than seeing someone dressed in
Orthodox garb eating in a restaurant with an unauthorized hechsher, or
no hechsher at all. Ignorance has many faces, and the less scrupulous
are willing to use our naiveté to their advantage ....
Source: Jerusalem Kosher News