There are many hechsheirim in today's world, but unfortunately, not everyone considers all of them to be on par with their standards. Nonetheless, I am assuming (and you may correct me if I'm wrong) that certain certifications are stringent enough to be considered acceptable by all.
What are examples of such certifying agencies?
(this has practical relevance for buying someone a gift, if you know they are stringent, but don't want to ask which certifications they accept)